imma push back against that just a little bit. the shape of ui elements, what sort of interactions a platform allows a person to make, are kinda arbitrary, and putting deliberate thought into how they are laid out is important. in real life social interactions, there is functionally no analogue for a like or dislike button. there are fully cogent arguments for not including "the power of users to be negative" that don't rely on suppression of speech or whatever, because that power is kinda exclusive to online platforms to begin with, and can allow larger groups to suppress the visibility of people they don't like. "being negative" in a social context is a tricky idea to pin down, and there are a lot of real life social contexts where "being negative" would be seen as anti-social.

in any case, a downvote is sorta equivalent to shouting somebody down, or interrupting somebody who's talking. depending on how its implemented, it might actually be a pretty potent tool as suppressing discussion. in certain contexts it might be useful, but any utility it provides is necessarily less than articulating why you disagree with somebody with a comment.