While not directly comparable, this is almost what StackOverflow does. They don't force you to comment, but if you downvote they ask you to comment and the community does not approve of random downvotes. Additionally, downvoting costs a bit of rep.
In all, this means downvotes are uncommon; usually, people try to fix the problem (editing or asking the writer to edit). However, if something is downvoted, it is extremely likely that that post is irrelevant or actively wrong.
In all, this means downvotes are uncommon; usually, people try to fix the problem (editing or asking the writer to edit). However, if something is downvoted, it is extremely likely that that post is irrelevant or actively wrong.