Although the debate on the origins of sexuality is interesting, I don't think it should be relevant to equal rights and what not. Even if homosexuality were a choice, it'd be a valid choice. I'm also of the opinion that sexuality is naturally more fluid, especially among men. In places like ancient Greece, same-sex relations between men were part of the normal socialization process, and many still ended up fulfilling their filial obligations later on by getting married to women and having families.
In traditional societies where homosexuality is not openly discussed, like in China, people are pressured into heterosexual marriage and nuclear families, but men are constantly having forrays on the side with other men. There is no real concept of "gay". People don't call themselves gay or straight. They simply do what is expected and then maybe have other pleasurable adventures with men OR women on the side.
After studying this for years and years, as well as living in foreign cultures, I think sexual activity is really layered and comes down to relational context. Personal pleasure, family and social expectations, cultural norms, level of openness and outness... in any one of these realms a person's sexuality may manifest differently. In the personal/private realm, people are doing all sorts of things including the so-called taboo; on the family level people are getting married to fulfill lineage obligations; on the cultural level taboos shape how open you can be about what it is you're into; laws govern how open you can be, etc.
When people look at JUST homosexuality as a concept, they are placing it in a vaccuum. They are also just looking at sex. Taboos against same-sex relations have consequences for even the so-called heterosexual. Men are not allowed to touch, to comfort one another, to engage in nurturing activities with one another, to express love and affection outside of the accepted ways, to be non-competitive, etc. In India there are men who hold hands walking down the street and they are not partners, they are affectionate friends.
Homosexuality is JUST about who you are having sex with. This entire debate should be about homo-relations. When you look at it in that context, sexual acts no longer have confining parameters. Someone who has sex with the same sex does not necessarily have to be gay, they could just be engaging in a social relationship.
The whole idea that people have to choose, and that choosing means a certain set of behaviours, is totally flawed. The western world and especially the United States need to get over this idea that there are "camps" for everything. People jump ship all the time, or are ignoring labels while simultaneously using those labels. It makes no sense.
