@sage When we block people, their posts appear as gaps in our threads. I can't imagine that deleting a post that violates server rules could be more disruptive than that.
If the rule they violated is worth having, can you really say "the harm was already done"? Isn't further harm done every time someone else sees the offending material—if not because of the material itself, then because a reader might easily conclude that offending material won't be dealt with?