Really, the sticking point is not whether a commenter should be able to repost their comment elsewhere. It's that, in the current setup, the commenter's crossposting does not protect the identity of the original poster. That could be fixed by transferring across the whole comment without giving a link back to the conversation to which the comment was a response, or showing the title of the post. You would then force the comment to stand alone outside the protected context of the entry, because the context does not belong to the commenter, but to the original poster whose business was being discussed under lock. Of course, it would then make crossposting very dull and fewer people would use it, because who wants to read an in-depth comment about some detail of Poster A's life when you can't find out who Poster A is and what the context was?