Is it a plastic surgeon's job to say "enough is enough"?

I’ve been reading about Heidi Montag and her recent plastic surgery . And I’ve been thinking a lot about her. Shallow and unimportant, I know. Some comments I’ve read online are from people asking what surgeon in their right mind would do this… but I wonder if it really is a doctor’s job to tell a patient what he or she can and can’t do to their own body.

Legally, what’s the answer? Are doctors allowed to perform on people with body dysmorphia or clearly unreasonable expectations such as being “perfect”?
What about ethically? If someone like Heidi Montag, Michael Jackson, or Jocelyn Wildenstein want to have more surgery, should a doctor be allowed to perform it?
What do you guys think?