I almost don't dare to say this, but I think the downvoting is flawed because there is nothing to prevent politically incorrect comments to be downvoted, regardless of their validity. To give one concrete example consider this comment:
http://lesswrong.com/lw/1ww/undiscriminating_skepticism/1r5v
All it provides is a link to a video with eye-witness testimony against a claim made on the corresponding post and it is relentlessly downvoted(-17 as of last counting). In a website devoted to rationality shouldn't it be a rule that you can't downvote evidence?
All it provides is a link to a video
It is a waste of time.
The video may be tiny, tiny, tiny evidence against the claim made. The fact that this was the video someone chose as evidence against the claim is a good deal more significant, and is evidence for the claim that overwhelms the tiny, tiny evidence.
Yet it still is a waste of time to present small evidence in favor of conclusions people already believe, even more so than it would be to bring infinitesimally small evidence against such claims.
People who go back and downvote every post or comment a Less Wrong user has ever made, please, stop doing that. It's a clever way to pull information cascades in your direction but it is clearly an abuse of the content filtering system. It's also highly dishonorable. If you truly must use such tactics then downvoting a few of your enemy's top level posts is much less evil; your enemy loses the karma and takes the hint without your severely biasing the public perception of Less Wrong's discourse.
(I just lost over 200 karma in a few minutes and that'll probably continue for awhile. This happens to me every few weeks. Edit: I mean it's been happening every few weeks for a few months for a total of only three or four. Between 400 and 700 karma lost total I think? I don't mean to overstate the problem.)