moi aussi,
You are correct for the most part (I think there was one study that found identical twins to be just over 50%). But almost all the studies did show that if one identical twin brother was homosexual there were higher incidences of homosexuality in the other identical twin brother than with non-twin brothers. This would seem to indicate some genetic factor.
jewishfeminist02,
While there are plenty of situations that are as you describe. There is no serious scientific basis for claiming that there is no sexual desire involved on the part of the aggressor.
Furthermore, not all homosexual encounters in prison are non-consensual. There are also plenty of consensual encounters by people who were, and return to being, heterosexual on the outside. The same thing occurs with women.