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.)
Unbalance between upvoting and downvoting. If downvotes had to be explained but upvotes not so, upvotes would become much cheaper, although they have the same nominal value. A fairly bad post which now earns 4 downvotes for each upvote could easily be in the positives then, with consequent encouraging of low quality posting.
If several people downvote for the same reason, they would nevertheless have to spell it out. So they would either refrain from downvoting if somebody had already stated their reason (and therefore posts with one substantial error would be in unfair advantage over posts with several different slight imperfections) or we would earn lots of nearly identical comments.
People would learn to overcome the technical solution. For example, after dowvoting, one can write simply "disagree". Or "no". Others could, of course, downvote such comments, but it would cost them much more effort, because they had to tortuously explain what's wrong (I assume answering a "no" by another "no" is silly).
Sometimes a troll or a crackpot appears, and then downvoting without explanation is really the appropriate tactic.
These are the costs, you have already stated the benefits.
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.)