It's not a secret that Progressives and Libertarians don't see eye to eye. They disagree very fundamentally about the role of government in every facet of life. It can then seem odd that occasionally there are certain topics where the two seem to agree where there's a problem. Most of these are in the civil rights arena, for example, the legalization of drugs, sex related issues like abortion and prostitution, and of course, they share a general distrust and sometimes downright hatred of police.
The obvious question is: where does this come from? How do two groups that so vehemently disagree on the fundamentals of government come together to hate the police? The answer is complicated, but when you get down to it, they really don't agree like they seem to.
After almost any incident where the police murder someone or just shoot seemingly for no reason, progressives and libertarians alike have critical reactions. The similarities end there however. Progressives react very emotionally, which is understandable to be fair, and libertarians respond viscerally sometimes as well. Reacting emotionally makes sense, the incident usually involves the murder of an innocent person. But a lot of libertarians, or at least the ones with more anarchist leanings are less emotional. They're more exasperated than emotional, and they have a kind of "what did you expect?" reaction. The progressive response is typically followed by a call to action, a reminder to their friends and family that they need to vote to implement change and end (racialized) police violence. This is where they're wrong.
Police violence is not a bug, it's a feature.
I'll restate here what libertarians, or at least anarchists, already know. Police needlessly murdering people with impunity was always going to be a byproduct of this system.
At least progressives recognize the epidemic of police murders, but they fail to see the big picture. Beyond the disproportionate amount of black and brown people killed by cops, the real universal underlying problem is that cops aren't just killing people because of individually racist cops (which I doubt is rare,) it's because this is what cops are trained to do. In every case where you see cops do obviously brutal and violent things, it shocks people because they just don't think about what cops do or a government is.
A government is just a monopoly on violence in a geographic area, and cops are just the thugs who enforce it. It's just a gang, like the mafia, or a cartel. Cops are the henchmen. But people (especially progressives) don't see government this way. When you tell them the end of the text of every law has an implicit "...or else we'll eventually murder you," they treat it as a joke, they truly don't believe that's what laws actually are. So when they see Eric Garner being choked to death for selling loose cigarettes, they can't believe that's what government really is, so they resort to other answers, which may explain why it happens to certain people (young black & brown men) more often, but doesn't explain the underlying cause.
Eric Garner was killed not primarily because he was black or a man or dressed a certain way, he was killed because that's what the government is supposed to do.
This is exactly how this system is supposed to work. So stop thinking "all we need to do is vote the right guy into office, and then we can remake the results how we want." Even if you get what you want, you will be disappointed.