• This explains why comments like "me too!" or "this is so cool!" (comments that are really only taking up space, or that could be expressed more succinctly by clicking the upvote button instead) get downmodded so consistently.
• Also, this provides the only valid reason for someone to delete one of their comments: If it becomes clear that the comment is only taking up space, or the conversation's SNR would be otherwise be increased by deleting a post, then it should (must?) be deleted.

I will sometimes liberally upvote someone's comment, just as a sign of respect. However, I only do this when they're likely to be downvoted, or soemtimes if they think they're likely to be downvoted.