Too many people are ignorant of this.

I have a belief (not based in law, just my personal feeling) that once you post something in a conversation in a public forum, you no longer have any natural right to control it. By posting it in a conversation on the public internet, you have, in a practical sense, waved any right to control it. That is a part of a conversation that belongs to the public, and you gave your comment away freely. It is public record. You cannot demand that it be forgotten or erased any more than I can demand that something I said to my friends yesterday be forgotten and erased.

If I hosted a forum, I would make it clear that this is the policy, and I would not allow people to delete comments that they posted. Edits would be allowed, but the history would be available. Deletions would only ever happen if I was legally compelled.

This all gets complicated if someone posts private information about a third party. I would rapidly delete such posts and ban such users. The third party never consented to anything, so it's not the same.