And comment reputation is also kind of meant as a protection against spammers or as some kind of method to detect people who aren't likely to post useful comments. People can up- or downvote a comment on a story or a blogpost in the first three days after it was posted, though recently the number of downvotes was limited to one for one person in 24 hours.

It's supposed to stop people from spamming other people's walls, you can set your wall on "unlimited messages" though if you don't mind getting messages.