Calm down everyone, blimey
Ok so, someone clicks 'like' on the thread
A link to the thread is posted as a 'like' on their FB profile
That person clicking 'like' will more than likely have nothing whatsoever to do with you, and no association with you whatsoever.
If you have mutual MN friends on FB with someone who 'likes' your post, then those mutual friends will see the thread - but they would have seen it on MN anyway.
People already can and frequently do c&p links to MN threads on FB
So again, what's the big deal?
It's a big fuss about nothing at all.
It's not like it's going to post on every facebooks users wall 'I liked this thread, and it was written by Jane Smith, who posts on MN as Janeyanyone and she lives at 101 Anyroad, Anytown, and here are her credit card details, and her bra size is 36C'