Those who oppose the ability to negate upvotes argue that it will allow censorship by opening up an easy way to silence a minority. The opposite is true: the negation of the need to negate upvotes is the actual censorship. You are effectively denying the validity of someone's need.
(image credit: www.thecepblog.com)
Arguments defending the status quo (where we have only one way to vote: upvote) boil down to this: we will open Pandora's box and negative behavior will prevail:
I personally don't like the concept of negative voting on a platform like this. I think it is too easy to abuse and just does not feel right to me.
On steemit currently 10 people could like my post and thus pledge value, and someone can come along and remove that value.
It's that negative voting isn't fun. It's not fun for people doing the negative voting a lot of the time and it's not fun for the people receiving the negative votes.
My question is this: what am I supposed to do when I see a weak post (it's my subjective judgement) drawing an excessive amount (again, my subjective judgement) from our limited funds? I feel the need to do something about it (as I have a share in these funds), but I can't.
Currently I have only two options:
- suppress my feelings and do nothing
- embrace my feelings and abuse the abuse flag (pan intended) and then feel bad about it (I've hurt the author's reputation and added my bit to the confusion about the flag's meaning)
So both choices are bad. I feel powerless even though I have Steem Power.
And now the anti-negative-vote folks come along and tell me that I am just being jealous and instead I should focus on my own writing or just find other stuff I like and use my Steem Power there.
So they tell me that it's good that the system does not allow me to exercise my will because actually it's just bad behavior. They remove the legitimacy from what I feel is right. I might be wrong in my judgement about the post I want to downvote, but the existence of my feelings is undeniable. Yet they silence my feelings because they know better. For me it's no different to censorship: instead of words we gag someone's feeling. And as such, it will backfire badly because it does not solve the problem, it just hides it.
What about giving the unsatisfied an easy way to vent their feelings? This way we don't reject them, they become part of the process, even if they are wrong. This way they can feel their vote matters a bit, is allowed and is treated on equal terms with the opposite view.
We are worried about negative votes silencing potential minorities, yet we blindly exterminate the existing minority: those who want to negate the payout.
Even if my feelings are negative and counterproductive, I should be able to express them by executing my will and be confronted with the outside world. Be exposed. But not be suppressed and told that what I feel is bad or will have negative consequences. If that's the case - let the world deal with it, instead of preemptively try to stop it.
If I vote to take something away from someone else then it damages the user experience not just for that someone else but also for everyone who witnessed me do it.
How do you know this? I really take it badly when someone tells me what's good for me and what's not.
Imagine this: you publish a post which says only this: "I need money to buy a new car" and some people, who happen to know you personally, upvote your post just because they are your friends. I see this happening and negate those upvotes. You, as the author of the post, are obviously not happy about it, but does it really damage the user experience for everyone who witnessed me doing it? I guess not. For them I'm the righteous one who prevented some kind of abuse. And it was an abuse by those who upvoted, not by you, the author of the post.
So no, we can't predict all the outcomes. We can only say that offering an extra option "damages the user experience" when it adds to the confusion, which is clearly not the case here. The case here is that we add a new dimension to the way people can interact with each other. So let them interact and sort it out among themselves. Otherwise we are playing a totalitarian game: we know better what's good for you.
The difference is that by casting votes affirmatively for one thing rather than negatively against another, we'll avoid causing downvoting wars and an otherwise nasty and cutthroat culture here.
Here is the thing: it's my certainty that I need this feature versus your speculation that this feature will be abused and will cause negative consequences. In other words, it's something that undoubtedly exists (unless you question my ability to define my needs) versus something that might come into existence but we can't be sure (unless you have some special ability to predict human behavior with 100% accuracy).
And finally something positive, a quote from 
Couldn't it simply be [that we] understood that downvotes have nothing to do with who wrote it or what it's about? Couldn't we educate ourselves to expect a rise and fall of post value with no cause to be butt-hurt? I know I'm a dreamer...
This is a beautiful attitude: first we need to make a leap of faith and arrange the system the way we want it to be in our dreams (so that it accommodates all our needs) and only when this proves to be an illusion (because of the flaws of human nature) we can reconsider and possibly go back to what we have now.
Let's not throw away a possibly valuable idea just because of our fears. It's our dreams that should drive our actions, not fears.
EDIT: After doing some introspection I think this is what disturbs me the most: we remove part of our freedom assuming it will have bad consequences before this fear was proven to materialize in real life. For me, limiting our freedom is a last resort, not a preemptive action aimed to yield to our fears.
But the biggest paradox here is that currently you are able to do what is feared by those who oppose the downvote option. You are just invited to do collateral damage to reach your goal.
This logic is completely beyond my understanding: even if we assume that lowering somebody's payout is damaging, it is preferred that you to do more damage (by using the flag), than give you an option to do less damage (by giving you a downvote tool).
To end on a more positive note, imagine how nice it would feel if some of the high-earning-by-default authors could do this: write a post, get all the usual upvotes to reach prime visibility and then after 24 hours just downvote their own post to release the funds. I don't expect them to do it, but having this option of self-downvote opens us up to the bright side of our nature, which is always a good thing.