So what action do you propose for a situation where some person writes an incorrect post and is then corrected, but the whole thread doesn't deserve to be upvoted?
If you just upvote the correction, you mark it as significant in some way. But if it's only correcting a flamebait, why would you? It seems to be better to leave the correction there (so that people who read it get more information), but force the whole thread to go down by downvoting the first incorrect post. I think it's a good protection against flamewars which may contain a lot of "correct" posts, but you may want to push them down anyways.
The problem of course is: what is correct / true and how sure are you about it.
Yes you're right. We each have our own definition of "better," as we do have for "correct." But it's less detrimental/errpr to just have you judge "better" than to have you judge both "better" and "worse" which is what happens when we allow judgements of "correct."
Because we can still sort comment by just up voting. But removing down voting would slow down the sorting process, therefore less power is there to disrupt the organization of comments.
I'll agree this may be viewed as one disadvantage of the system, but it also means there is less power in the individual to to push down the comment. It would require a bunch of up votes all the other comments in order to push down a comment.
That's why letting people to only up vote is less capable of silencing an opposition or unpopular view.
If you just upvote the correction, you mark it as significant in some way. But if it's only correcting a flamebait, why would you? It seems to be better to leave the correction there (so that people who read it get more information), but force the whole thread to go down by downvoting the first incorrect post. I think it's a good protection against flamewars which may contain a lot of "correct" posts, but you may want to push them down anyways.
The problem of course is: what is correct / true and how sure are you about it.