I think Michelle's answer is excellent, and I joined the global meta to upvote the suggestion to rename the "add a comment" link. Also, I think the suggestion in Michelle's answer to hide comments when some criteria is met is excellent because I think there's a piling on effect once an answer gets a couple of comments.
Interestingly, joining the global meta reminded me of my issue:
I think comments are somewhat specific to the topic at hand and don't necessarily agree that participation in another stack necessarily indicates a user's understanding of the rules sufficient to start commenting on every topic. I think we get a lot of low participation comments for a couple of reasons:
- The immediate points bump in excess of the comments threshold (but not the downvote threshold) for participation on other stacks
- The fact that you can comment but not downvote leads relatively new users to comment negatively because they can't downvote
- The lack of a downvote feature for comments
- The inability of a question or answer author to remove a comment that's been addressed
I'm sure a lot of people thought a lot about the arrangement of this list. I think that if there is a method for punishing bad answers, there needs to be a method for punishing bad comments. And, I may speak for myself here, I'd rather get downvotes than a comments expressing the commenter's opinion rather than to suggest a specific improvement.
A comment, by the stack exchange definition, is meant to address the author of the question or answer. I almost think a solution is not a rep level required to leave a comment, but a rep level required to see a comment. Either you wrote the question or answer and the comment is pertinent to what you wrote, or you're of sufficient rep to participate in moderating/editing questions and answers. This obviously leaves the possibility that multiple comments with the same suggestion will be left but to some extent I think the fact that comments are public invites opinionated comments rather than useful ones, then the opinionated comments invite further comments and a discussion. I think if comments were primarily invisible or visible only to those who could actually affect the edit suggested there would be no point to leaving a comment of opinion.
Ultimately if comments must be public, I think the core of the problem is that comments are "free." There's no "bad comment" stick the way there's a "bad question/answer" stick, I'll never lose my precious rep points for continuously posting useless comments.