The ability to arbitrarily and retroactively remove all traces of yourself from a discussion you had in public, via a quasi-persistent medium has always felt to me like a violation of everyone else in the discussion, but I, too, come from the forum space, where you just don’t do that. The microblogging space doesn’t seem to care, and the microblogging space currently dominates fedi. It kind of feels like a culture clash to me, and one of many reasons why forum-fedi and masto-fedi probably don’t need a whole lot of cross-over.
I know there are safety concerns around harassment campaigns and the like, and things should change and evolve in response to stuff like that. And it’s not at all clear to me how something like this interacts with the EU’s Right to be Forgotten. But forum users posting on forums, though distributed, are much less likely to be a disruption to those forums than masto users who don’t even know that they’re posting on forums, while behaving in ways that are normal for their space.
Mastodon is also somewhat hostile towards new users. Significant swaths of it treat this shared public network as a small private chatroom, and get cranky when September stretches on too long.