@Sollace
Personally, I think anyone should be able to downvote anything for any reason as long as they don’t try and do it with multiple accounts or gather others to mass-downvote (and those are bannable offenses themselves anyway). Each person can only change the score by one point, after all, and the score has no practical effect on the image besides reflecting its popularity. Spamming negative comments on images just because you dislike their theme is another matter, since that can actually disrupt the comments section, but a downvote is just clicking a button and changing a number by 1. It shouldn’t matter that much.
There’s no restriction on upvotes, so it’s always felt like restricting one kind of vote and not another artificially inflates the score of some images. Especially since the whole “don’t downvote what you can filter” thing is
extremely restrictive if you follow the logic through to its conclusion, what with there being a tag for virtually everything on Derpibooru, including low artistic quality in several cases. If one actually followed that principle universally, the downvote button would be virtually unusable.
I realize this is a bit off-topic, so there’s no need to turn it into a lengthy debate, but it’s a site policy that’s never sat right with me.
Knowing the mods have tried to outright remove the button before doesn’t make it easy to trust the motives behind the rule, either.