I vote that they stay. They're very easy to ignore if you choose and they're fun if you don't.
Doesn't bother me in the least to get a thumbs down.
Also it seems that a lot of times a good post will get a lot of thumbs up, and sometimes they're on posts by people who don't post a lot and sort of went out on a limb expressing something. Those always make me smile, as it's a nice way of the whole group showing that they appreciated it, and I think that encourages people to post more & better posts.
You can tell the harassers - those who thumbs down an innocuous post out of spite, and that just tells you you did a good job.