Another example of the "gay to straight" myth

[Mystical]

I don't know if conversion therapy is effective or not. However I do ask myself if pedophilia can be treated why can't homosexuality? Further if someone wants to be treated for homosexuality....why should we prevent it?

Yes, it is known to cause documented psychological harm to deny ones own sexuality.
Thankfully, people far smarter than you or I do have answers to your questions.

"Our AMA… opposes, the use of 'reparative' or 'conversion' therapy that is based upon the assumption that homosexuality per se is a mental disorder or based upon the a priori assumption that the patient should change his/her homosexual orientation." H-160.991, Health Care Needs of the Homosexual Population.

"Psychotherapeutic modalities to convert or 'repair' homosexuality are based on developmental theories whose scientific validity is questionable. Furthermore, anecdotal reports of "cures" are counterbalanced by anecdotal claims of psychological harm. In the last four decades, "reparative" therapists have not produced any rigorous scientific research to substantiate their claims of cure. Until there is such research available, [the American Psychiatric Association] recommends that ethical practitioners refrain from attempts to change individuals' sexual orientation, keeping in mind the medical dictum to first, do no harm.

The potential risks of reparative therapy are great, including depression, anxiety and self-destructive behavior, since therapist alignment with societal prejudices against homosexuality may reinforce self-hatred already experienced by the patient. Many patients who have undergone reparative therapy relate that they were inaccurately told that homosexuals are lonely, unhappy individuals who never achieve acceptance or satisfaction. The possibility that the person might achieve happiness and satisfying interpersonal relationships as a gay man or lesbian is not presented, nor are alternative approaches to dealing with the effects of societal stigmatization discussed.

Therefore, the American Psychiatric Association opposes any psychiatric treatment, such as reparative or conversion therapy which is based upon the assumption that homosexuality per se is a mental disorder or based upon the a priori assumption that the patient should change his/her sexual homosexual orientation." Position Statement on Therapies Focused on Attempts to Change Sexual Orientation (Reparative or Conversion Therapies).

Since the 1970s, the consensus of the behavioral and social sciences and the health and mental health professions globally is that homosexuality is a normal variation of human sexual orientation, while there remain those who maintain that it is a disorder. [U][2] In 1973, the American Psychiatric Association declassified homosexuality as a mental disorder. The American Psychological Association Council of Representatives followed in 1975. [3]

Thereafter other major mental health organizations followed and it was finally declassified by the World Health Organization in 1990. Consequently, while some still believe homosexuality is a mental disorder, the current. research and clinical literature demonstrate that same-sex sexual and romantic attractions, feelings, and behaviors are normal and positive variations of human sexuality, reflecting the official positions of the American Psychiatric Association and the American Psychological Association.[/I]

Paedophilia on the other hand is considered a paraphilia, along with 500 other things such as necrophilia, exhibitionism, voyeurism, sadism, masochism,etcetera.
Ever spanked during sex? Enjoyed a good lap dance? Wanted to show your schlong to someone? Paraphilia. Not sexuality.

In the current version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), a paraphilia is not diagnosable as a psychiatric disorder unless it causes distress to the individual or harm to others. [1]
Paraphilias are currently recognized as one of the categories of Sexual and Gender Identity Disorders in the DSM-IV-TR (Diagnostic and Statistical Manual of Mental Disorders - text revision, 2000)