The most common theory i've heard regarding this line of thought is that homosexuality genes produces a dead line for males, but it produces extraordinary fertility in females, and because of this, the genes more than make up for the deficit they cause when inherited by males.
I'm thinking there might be a genetic component in some cases, (effeminate males with effeminate personalities) but I think in many if not most cases, homosexuality is often the result of child abuse. One study i've seen asserted that 40% of homosexuals admit to being molested as children.
Something else to remember is that most “homosexuals” are not exclusively so, but are in fact bisexual.
There are some rather strong genetic interactions with this, with the main ones being whether one is selective or not. In other words, the scale is not so much heterosexual at one end of the scale and homosexual at the other end of the scale; but rather discriminating at one end of the scale and indiscriminate at the other end of the scale. Another genetic factor appears to be the strength of the monogamous/polygamists tendencies.
Homosexuality appears to be primarily a miss-imprinting on those factors, primarily through trauma..