Here is a link to an American Medical Association presentation from January 2011 that provides incredible statistical and biological data that demonstrates that gender identity and sexual orientation are very largely formed from nature, not nurture, and that further, attempts to change either of the above are highly likely to fail.
The presentation is about an hour long. It’s filled with the latest data on hormones, biology, fetal development, and brain structure. It provides an excellent theoretical basis that explains why homosexuals are as they are, as well as why transsexuals are as they are.
People who deliberately ignore this sort of data are the equivalent of the Catholic Church attacking Galileo. Myth and superstition have no place superseding science on matters so critical to human physical and mental health.