Downvotes signal "would like to see fewer comments like this one". This certainly applies to trolls and nonsense, but it feels appropriate to use the same signal for comments which, if the author had taken a little more time to compose, readers wouldn't need to spend time correcting one way or another. The calculation I've seen at least once here (and I tend to agree with) is that you should value your readers' time about 10x more than you value yours.

The appropriate thing to do if you receive downvotes and you're neither a troll nor a crackpot seems to simply ask what's wrong. Complaining only makes things worse. Complaining that the community is exhibiting censorship or groupthink makes things much worse.