@DForck42, after reading through all of this site’s Meta posts, all I can say is that I have abiding admiration for your contributions (and others’ for that matter). That is why I read and re-read everything you said here.
I have seen all sorts of comments on all sorts of questions, ranging from unveiled humor – to pointing out mistakes – to refining someone’s good answer – to you name it. My guess is that if we attempted to categorize comments, we would ultimately find that we cannot meaningfully do so. So I say why try?
The only hard and fast rule I can come up with regarding a comment is: If it’s not rude and it helps somehow, then it is probably OK. So rudeness should be deleted. “Thanks” should be deleted. A comment with a mistake should be addressed like an answer with a mistake: with a comment. But if it helps the post, whether it’s a question or an answer, then it is probably OK. Of course, this begs the question of what is helpful (which leads to subjectivity in answering this and the reason for your post). Another factor I would mention is to consider the intent of the commenter.
Not providing answers as comments.
Sir, I cannot say I fully agree with this. By example: if a good answer requires five pieces of information, but I only have two, should I answer. I think not, but I also think that withholding this is incorrect; and putting that information in a comment is helpful. Someone else may have the other three pieces, and the result will be a good answer. If you have something to contribute, and an answer would be substandard, then please present it in a comment.
Flagging such comments.
Is there a lot of grey area here? Yes, as you’ve aptly pointed out in the examples you provided. Ultimately we have to deal with it using good judgment. And flagging is the way to go, if needed.
Monsters from the ID
Now to get to the “everybody-is-sensitive-about-this-issue” issue: How does that apply to ID questions? There are people who have been searching for decades for a title (and I am one of them). Honestly, if a question is doomed for closure in the near future (future tense/sense), then what is the real harm is providing a suggestion to check into via a comment – as the question is processed off the site? You might say we are rewarding the undeserving. OK. But how does that even begin to compare to the PROFOUND assistance and satisfaction that we are giving some people in need (with just a few keystrokes as a question proceeds to the dust bin)? [This assumes the suggestion was right. But who cares?]
On the other hand, an acceptable ID question should be answered in the answer section, even if it’s a guess. And as a side note, we should NOT post answers to unacceptable ID questions.