OK, feel free to reword it to "upvote the comments you want to see discussed more". My main thrust is that an explicit guideline should be given for comment moderation, not what the exact content should be.

Usually it's comments I disagree with that I want to see discussed more. It's where someone else disagrees with you that you are most likely to identify mistakes in your own reasoning. Reading things you agree with can make you feel all warm and fuzzy, but you won't learn much from them.