Downvotes without an explanation have no meaning. You should be required to explain why you downvoted.

If a downvote means "I'd like to see fewer comments like this" -- then, why? What is wrong? Is it off-topic, rude, you disgaree, it used words you don't like, it ran on too long. What, what, what is the problem?!?! A downvote gives you nothing but some vague feeling that you broke some kind of social rule or norm somewhere _without actually explaining what it was you did_

Downvotes are mostly non-useful and promote "safe" comments, which have a tendency to be boring.