I agree that people who say "more honest internet" are usually trying to make a virtue of necessity; but its not entirely untrue.

Re-writing one's posts to make replies look off-target / ridiculous was a common enough forum tactic in the late 1990s and early 2000s. Forums would often set posts immutable after a few minutes to limit this.

On balance I think clients and relays should honour deletion requests, but self-doxxing and foot-gunning will remain major risks whatever we do. 

"The bad people" can easily store everyone / everything of interest to them and ignore deletion requests.