I do like the idea of disabling comment editing on a post with new comments enabled; "I don't want anyone to talk to me about this anymore" *means* "I don't want anyone to talk to me" not "I want you to edit your existing comment into another 5,000 words worth of wank that nobody can reply to, inculding cussing me out for disabling comments."

...you can see the problem, right? If comment editing is left on, it means that people who actually want to freeze all comments would have to use the old behavior.