I think HackerNews obscures/hides posts when they hit a certain number of downvotes. Maybe try something similar? We'll see fewer negative comments, plus it'll protect people who might have been unfairly downvoted from taking a big hit.

I'm also pretty sure HN users cannot vote until they hit certain thresholds. Upvoting requires 10 points (?) while downvoting is after 100. Finally, I think voting is removed after a period of time, like 2 weeks.