How often here on HN or anywhere else do you type a comment and not submit it, because in the end you think it's not insightful enough, too controversial, too political, too inflammatory or any other reason?
Somewhat often. One of the moderators here, dang, reminded me once that if I made a good/insightful comment, and that someone else responded with a bad argument, people would see both, and judge accordingly, so there's no reason to engage in further argument with someone else if there's nothing else valuable to contribute to the discussion.
Sometimes I type up a response to someone, and before sending it, realize I'm not really adding anything new after re-reading it, just reiterating that someone is wrong, and I delete it.
(edit) One thing I do a lot of, shamelessly, is clarifying edits. If after seeing a couple comments, I feel my comment is missing something that would've addressed the replies better, or if I felt like my point was misunderstood, I'll fix it. (edit2) It's somewhat common for me to post a comment and then edit it to add more thoughts a minute or two later.
Sometimes I type up a response to someone, and before sending it, realize I'm not really adding anything new after re-reading it, just reiterating that someone is wrong, and I delete it.
(edit) One thing I do a lot of, shamelessly, is clarifying edits. If after seeing a couple comments, I feel my comment is missing something that would've addressed the replies better, or if I felt like my point was misunderstood, I'll fix it. (edit2) It's somewhat common for me to post a comment and then edit it to add more thoughts a minute or two later.