If a young girl was molested repeatedly and developed abnormal feelings towards men as a result, can't you see that therapy addressing her sexual orientation and behavior might be appropriate? There are other scenerios. It is therapy for those who WANT it. To deny them that seems cruel to me. You can still argue that others neither need, want or are capable of change (I probably won't agree, but will concede I haven't proven it beyond any doubt).
Given that I don't consider celibacy a "success", unless you're training priests, nuns, or monks, I do believe that some people can change homo- to heterosexual, and vice versa. More than just getting married and having children, or being Bubba or Bubba's b!tch in prison.
I think it's rare, but possible. There's been too much propaganda and not enough research to make therapy as effective as it could be.
If a patient goes in saying "this is what I want", then the therapist should try to help. I don't think it's fair to tell a homosexual who wants to change that he has to figure out how to be happy as is, but likewise, it's not fair to tell him that whatever his current situation or past history is, he has to be heterosexual before therapy is complete.