If it is OK to pretend that your boy body is a girl body (or the other way around) and we are all supposed to go along with it, why not pretend that your fat body is a Barbie-body?  Or a better question is, at what point does your body dysphoria become a mental illness?  We treat people who have anorexia rather than "support them" by helping them to lose another 10 lbs.  Shouldn't we be happy with the bodies we have and not be so easily influenced by external forces?