The most obvious danger is that after the sex change operation the person will discover him or herself irretrievably and vitally maimed and then decide she made a mistake (both from a psychological and physical point of view). The problem is, of course, that this mistake cannot be corrected. Tennis star Renee Richards (formerly Richard Raskind) often expressed second thoughts over a 1975 sex change operation and is quoted as saying, "Better to be an intact man functioning with 100% capacity for everything that to be transsexual woman who is an imperfect woman." (The Lady Regrets, NY Times, Feb. 1, 2007.) Of course, the same statement would equally apply for a woman who desires to be a man.
A most interesting website to review is http://home.vicnet.net.au/~gendmend/About.htm. It was written entirely by individuals in Australia who underwent sex change operations and then realized that they had made a tragic error. The organizers of this group now try to warn individuals contemplating sex changes about the pitfalls and tragic consequences that can result from the administration of cross-sex hormones and surgical sex modification procedures. They also seek to encourage these individuals to seek independent advice from suitably qualified medical practitioners.
One of the founders of "gender menders" (the group who organized the web site above) is Alan Finch. He publicly stated, after going through 2 sex change operations (the second one an attempt to reverse the first one) that the key to dealing with the gender issues is to work with the psyche, not the body, and to rebuild the patient's damaged and incomplete internal identity rather than perform the kind of drastic surgery that damaged him for life.
Based upon his own personal experience, Alan Finch rejects the notion that a transsexual is a "woman trapped in a man's body" or "a man trapped in a woman's body." These notions have been transformed into such a cliche that transsexuals themselves can no longer be sure whether they actually feel that way or whether they are merely repeating a socially implanted mantra.
When Johns Hopkins University closed their sexual reassignment surgery center, the head psychiatrist, Dr. Paul McHugh commented, "We psychiatrists, I thought, would do better to concentrate on trying to fix their minds and not their genitilia." (Surgical Sex, p. 35)