I don't typically downvote. I know others do for plagiarism and that's fine but some of the down detectors seem to actually get it wrong sometimes and at other times seem to use it because content goes against their own standards.

However, serial downvoters and people that set up accounts that downvote and put spam auto comments on people's posts that have nothing to do with their content, i will downvote them at any chance i get.

Interesting question, thanks for asking.