I would be ok with that as long as the original is kept whole and visible. That would make the edit a correction, and a separate post. Deletions I would also not really want, although an "ignore me" flag might be useful. That way someone could regret a post and flag something as "ignore" and clients who had the setting to ignore posts with those flags wouldn't show them. But I still consider it important that people take responsibility for what they post and be held accountable for it.