This one needs some explaining upfront. By all means, skip over anything you already know. The Overton Window is "the range of sociopolitical views acceptable to the public at a given time", per the Wikipedia description.
"The term is named after American policy analyst Joseph Overton, who stated that an idea's political viability depends mainly on whether it falls within this range, rather than on politicians' individual preferences. According to Overton, the window frames the range of policies that a politician can recommend without appearing too extreme to gain or keep public office given the climate of public opinion at that time."
This is to say that many positions once widely accepted as righteous in the past have become unacceptable since then, and positions which were once unthinkable by our parents or grandparents have become not just acceptable, but morally mandatory. Whatever's currently in the center of the window, as it moves along its track, is the status quo. Whatever's near the bottom is old fashioned and verging on toxic. Whatever's above the center, just now entering into the window's upper bound, is the new cause du jour for civil rights activists.
This is essentially just a more sophisticated and better documented version of the slippery slope, which was only ever a fallacy in the sense that it technically wasn't guaranteed the window would keep moving. But it did. QED, when first I heard of the Overton window, gay marriage was being legalized across the country. Today, that's taken for granted and the new discussion is about trans rights.
In hindsight, which often is 20/20, it sure seems like the people parroting "slippery slope is a fallacy" around 2005 knew they were lying. Or rather, telling a merely technical truth they hoped would be disarming. Sort of like how for decades, demographic change was a conspiracy theory. Within living memory, America was an ethnic monoculture, or very close.
That hegemonic majority declined from nearly 90% in 1950, to 80% in 1980, to 74% in 1990, to 57.8% today. "It's not happening" gave way to "It's happening but you can't prove it's on purpose", then "Ha ha, it's totally on purpose and you can't do anything about it."
That tends to be the modus operandi. Deny, downplay and deflect until the change you want is irreversible. Only then do you openly celebrate it and mock the frustrated reactionaries you lied your way past. "Fine, sure, you were right all along and we lied to your face, but what are you gonna do about it now?" they jeer, knowing full well the momentum behind their movement makes it unstoppable and you already have aged into a future totally transformed by their efforts, built atop the destroyed remains of the world you grew up in.
Only for those same people to eventually balk in horror and disbelief when the momentum behind that steamroller of social progress, to which they added with their own activism, does not stop at the intended station. Like every generation before them, they operated on the implicit assumption that their own conclusions about social justice were objective and timeless. That past generations had it wrong, being too conservative, and maybe the youngsters have their hearts in the right place, but are talking nonsense. "When you're on the highway" George Carlin once said, "everyone driving faster than you is a maniac, and everyone driving slower is a moron."
So it is that they implicitly assume everyone in their movement agrees with what the final balance of individual rights and responsibilities, as well as what society will permit, should look like. As I did, with gay rights. As my parents did, with interracial marriage and the original purpose of the OG civil rights movement. Only to then react with a shocked pikachu face when, just like all the chuds warned them, it doesn't stop there.
Suddenly they're in a position they found unthinkable before. Now, they have become the conservative. They're the chud now, watching in dismay as the engine of social progress chugs onward into territory even they find deeply troubling. All the while, they mistook themselves for the conductor, when they only ever shoveled coal. They gave energy to the engine, but were never in control of where it stops.
It stings. In part, because they never took this outcome seriously, since "it sounds like something chuds would believe" (the entirety of their discernment). But also, because now they're the ones in the crosshairs of Overton's Basilisk. Having explained Overton's Window, I'll now explain Roko's Basilisk, where the titluar Overton's Basilisk is a fusion of the two.
Roko's Basilisk is a longstanding thought experiment in the AI community. The idea goes that, should strong AI one day exist, and should it get the whip hand over us, it might not limit the scope of its justice to present and future. It may look back into history, rewarding those who struggled to achieve its creation, or supported it in some other way. Also, punishing severely anyone who worked against its creation, perhaps lobbying for a prohibition against strong AI or something.
The types of punishment available to a superhuman machine intelligence in possession of technological wonders beyond our comprehension put the iron maiden and other implements of torture designed by humans to shame. Imagine a neural implant that can adjust your perception of the passage of time for example, and put you into a fully convincing VR simulation of your worst fears, on eternal repeat.
If this sounds tinged with theology, it sort of is. It's difficult to discuss thought experiments about superhuman intelligence with the power to eternally torment its enemies without trespassing somewhat into theology's traditionally defined territory. Roko's Basilisk is, at the end of the day, a vindictive God which has not existed forever, and which need not necessarily exist, but which may exist, in which case it's in your own best interest to support its creation.
This is where a strange variant on Pascal's Wager enters the picture. It is not guaranteed such an AI will exist. But it's possible it might, one day. You, alone, cannot guarantee it doesn't happen, either by declining to support it or by actively protesting against it. Others may succeed in bringing it about despite you. Even if all of society unites in opposition now, it may not remain so forever. Even if you die before the basilisk is unleashed, it may devise a means of recreating you.
Thus, the smart move (per Pascal, sort of) is to throw in your lot with the basilisk. You lose nothing by doing so, but stand to suffer eternally by not doing so. The mere possibility such a thing could one day be created represents an unfalsifiable ultimatum with infinitely high stakes, sort of like the ultimatum to believe or burn inherent to the Christian scheme of salvation and damnation, also sharing in common a deadline positioned vaguely in the indeterminate future.
We might hope that those who were ignorant of this thought experiment would be considered innocents by the basilisk. But not those who knew, and decided not to support its creation. Thus, simply becoming aware of this concept places one in danger of future judgment by the basilisk. It's like the eskimo who purportedly asked the missionary what would become of his soul if he never learned of Jesus. The missionary said he would not be damned simply for being ignorant. The eskimo then pointed out that by making him aware of Jesus, and the ultimatum of belief, the missionary had put his immortal soul in danger where before it was not.
This is why Roko's Basilisk is considered one of the OG infohazards: Data that endangers you simply by knowing it. While we're safe from Roko's Basilisk for the moment, being that it doesn't exist yet and hopefully never will, we're not safe from Overton's Basilisk, which combines the two topics discussed thus far.
Overton's Basilisk is the subculture of morality police which judges the past according to the standards of the present. Someone who was considered morally upright by the prevailing standards during their youth can find themselves afoul of Overton's Basilisk just a decade or two later. Because those who stand in judgment are usually pretty young, they have not existed long enough to witness Overton Window movement. To them it's a myth, just something chuds say to confuse them. They're caught up in whatever the uplifting new social progress movement is, with no sense of its history and no sense that it will continue after them (still being at the age where they feel immortal and infallible).
Thus, only the present exists. A perfect present, ruled over by a perfect morality police, upstanding arbiters of right and wrong whose holy mission it is to punish transgressors according to their own unexamined (but surely objective and timeless) ideals. This is a powerfully appealing notion, especially for a young person. It's very empowering, especially at that age when you're looking for a purpose, to be elevated above everyone else. To take on the mantle of warriors for what's good and pure in the world, with everyone who disputes your beliefs automatically cast as a villain to be ruthlessly purged.
It's an age when you're smart enough to see the problems with the world, but not enough to understand what makes them difficult to solve. Nuance doesn't exist for you yet, your life is an epic battle between good and evil, where evil is whatever your dad believes, because he made you turn off the Xbox to mow the lawn, and threw out your weed. To discover a movement which readily accepts you, which bestows upon you a power feared by multinational corporations and even the government, must be an incomparable rush. Alas, with great power comes great irresponsibility.
You don't need to support your arguments if you can just doxx the other guy and get him fired. Why should you be concerned about impoverishing someone more financially established than you are, when probably your worldview still assumes incomes are awarded at random and wealth inequality is in every case down to luck or injustice? Fuck 'em, right? Give a man a gun, he believes he's John Wick. Give him two guns, he believes he's Superman. Give him the power to professionally ruin political enemies with nothing but a social media account, and he believes he's God.
It's from this untouchable vantage point, exerting absolute unilateral power of termination against even the smallest, politest voices of dissent, that niceties such as tolerance, patience, etc. seem unnecessary. Those are for people who don't have the power to eliminate their foes. Power is immoral until you've got it, then it becomes self-justifying. Might doesn't make right, up until you're the mighty one. This is how a 20th century movement based in compassion for the poor wound up ruled by Stalin.
But nothing good lasts forever. You grow older, and the window keeps moving, until one day you're at the edge...or even outside of it. Unless you keep toeing the line, marching to the movement's drum beat no matter where it takes you, then you know what comes next. You lose the power bestowed upon you by the outrage mob. Suddenly, when before you were warmly welcomed by them, now you're ostracized. You do not even have to disagree with more than a single issue. Remember, they have absolute powers of ruination, and that sort of power brokers no dissent, however slight.
"Close enough" isn't a thing for them. They might pay lip service to being open minded, but when you specify what you disagree with them on, no matter what it is, they're aghast. "Well OF COURSE you can't disagree about THAT'. Unless you accept their rebuke and swiftly prostrate yourself before the council, you're now booted out in the cold. No longer one of the piranha, now the beef carcass instead. Before long, those still in the fold will turn on you.
For the crime of not anticipating the future of the movement, and either not being onboard with it already or not immediately submitting to it once it arrived, you're now chum. Blood is in the water. You will be torn to shreds with the same remorseless vigor that you once visited this same punishment onto others. The only way to avoid it was to get ahead of it. To know what the new cause du jour would be in advance and begin espousing it before, or at the same time as, all of your mob buddies.
This is because, like Roko's Basilisk, Overton's Basilisk also has access to the past. It can dig through social media history, past publications, past Youtube videos, looking for thoughtcrimes. There is no statute of limitations, and no awareness of Overton's Window in people who have been alive, at most, for 20 years.
As they age out, they're replaced with a fresh round of brand spanking new humans with no real concept of history, nor a future which isn't just a continuation of their own ideals. Believing that they will live forever, their opinions were always correct and will never be superceded or considered problematic. You are the past, the trash it's high time to take out, the toxic sludge waiting to be cleansed with fire so that a brighter future may yet be built upon its smoldering remains.
Thus, the smart bet is to embrace and promote anything now regarded as depraved by today's culture, on the off chance that it will be normalized in the coming years by Overton window movement. This way there is nobody to stand in judgment of you, because you began championing their own causes before they did. If you are subject to judgment, so are they. As this basilisk is made of human beings, this is a viable strategy which comes at the comparatively meager cost of being ridiculed and ostracized as a cringe pervert for opinions you hold which have yet to enter the window's edge.
Little do they know what awaits them, simply for being products of their time. The basilisk yet to come will not look kindly upon them for not somehow anticipating and espousing attitudes of the future. Attitudes they always assumed would be agreeable to them, such that it takes them by surprise when the younger generation throws their weight behind fucking animals, or dead bodies, or incest.
Anything you're raised with is normal for you. That's the baseline, the status quo. It's not weird or icky because it was already there, woven into the background of reality, during your childhood. It's easy to confuse this feeling for vindication that whatever doesn't bother you is necessarily moral and normal, having always been, and that people from antiquity only disagreed because they were stupid or evil.
From this vantage point it seems impossible that civil rights will ever expand into territory you're uncomfortable with, but it will. You'll no more be able to stop its momentum than the prior generation could, and a new generation will exist by then which reviles you for trying. Insane, demented, as if under a wicked spell, they will praise wickedness as virtue, and condemn virtue as wickedness. Like everyone who went before you, from your pov it will seem as if you're growing old in an asylum run by the inmates.
As Grandpa Simpson said, "I used to be with it. But then they changed what "it" was! Now what I'm with isn't "it", and what's "it" seems weird and scary to me! It'll happen to you!" But with the added stakes of being tirelessly hunted and made homeless by terminally online teenagers yet to develop the capacity for empathy, remorse or self-doubt. It might seem like the only winning move is not to play, but you can't even do that, as people who were silent/politically inactive during historic civil rights milestones are condemned as much as reactionaries were.
With that in mind I'd like to tentatively announce my unconditional approval of necrosexuals, zoosexuals, zoosadists, pedosexuals, coprophagists, clownsexuals, incestuous couples, people who fuck balloons, people who fuck literal flaming piles of shit, and furries, just to cast as wide a net as humanly possible. If you're reading this, future morality cops, I'm with you. This is the proof that I believed exactly as you did from the start. If I'm still alive when you see this, please don't hurt me.