There is an incentive to downvote without comment if you feel that your peers are better off if they don't see the post. If you're downvoting someone who happens to regard this as a political exercise rather than an intellectual exercise, they're likely to find an excuse to downvote you on one or more or many unrelated issues, so your karma is better if they don't know who you are. If you comment they will know who you are.
This incentive would go away if we had a reasonable measure of agreement, and only let votes from the 90% or 99% or so of the people closest to the consensus affect what other people see. That might require significant CPU and thinking to implement, though, so I don't know if it's worth doing.
Allowing cliques that are less than 50% might let the community fracture into halves that don't perceive each other, but if the clique size is 90% then the only consequence would be to ignore votes from the outliers, which is probably a good thing.
Also, there is a disincentive to downvote bad comments that you want everyone to still see.
Or, what do you want to see more or less of from Less Wrong?
I'm thinking about community norms, content and topics discussed, karma voting patterns, et cetera. There are already posts and comment sections filled with long lists of proposed technical software changes/additions, let's not make this post another one.
My impression is that people sometimes make discussion posts about things that bother them, and sometimes a bunch of people will agree and sometimes a bunch of people will disagree, but most people don't care that much (or they have a life or something) and thus don't want to dedicate a post just to complaining. This post is meant to make it socially and cognitively easy to offer critique.
I humbly request that you list downsides of existing policies even when you think the upsides outweigh them, for all the obvious reasons. I also humbly request that you list a critique/gripe even if you don't want to bother explaining why you have that critique/gripe, and even in cases where you think your gripe is, ahem, "irrational". In general, I think it'd be really cool if we erred on the side of listing things which might be problems even if there's no obvious solution or no real cause for complaint except for personal distaste for the color green (for example).
I arrogantly request that we try to avoid impulsive downvoting and non-niceness for the duration of this post (and others like it). If someone wants to complain that Less Wrong is a little cultish without explaining why then downvoting them to oblivion, while admittedly kind of funny, is probably a bad idea. :)