You can only downvote once your own comments have been upvoted a bit. Keep in mind though that you should only downvote for abusive comments (which also deserv

You can only downvote once your own comments have been upvoted a bit. Keep in mind though that you should only downvote for abusive comments (which also deserve a flag), gross misinformation, or other things like that. Disagreeing with someone is not a good reason to downvote.