You may be interested in the research of Dr. Paul Cameron. He is controversial in the ex-gay movement for his theory that a homosexual orientation is largely the result of personal choice. He denies the popular theories of "family dynamics" and "gender confusion" causing homosexuality.
A few excerpts:
"...Rather than gender confusion, FRI believes the facts show that homosexuality is largely about an obsession with sex and self-centeredness, and a desire to rebel against society, ones family, etc... We would argue that these same mechanisms also account for most of those who take up smoking, drug abuse, or other common bad habits."
I am wondering about this assertion about Dr. Cameron. It certainly doesn't fit with what I've read.