I read somewhere that flagging posts put a strain on the moderators, as they have spend extra time deciding if the flags are valid or not. Generally, we can either close questions, or downvote answers (as well as questions).
However, the thing is, we can't do that for comments. There sure are comments out there that are lousy enough, and the only remedy is to flag them,(which puts a strain on moderators, and I am repeating myself).
Would downvotes on comments help?
You can down-vote an answer, but the only way to delete something that has been posted as answer but that was supposed to be a comment, or an edit for the question, is to flag it for moderator's action. As some of the flags are exposed to 10k users, moderators are not the only ones who check if a flag is valid, or not.
Down-voting an answer and flagging it are two different actions; you down-vote an answer that is wrong, such as an answer that reports that punctuation is composed by punct + ation, but you flag it as "not an answer" if the question's author wrote an update of the question as answer.
In the same way, down-voting a comment would be different from flagging a comment. As comments are not first citizens, down-voting them would not have any purpose.
