If you cut through all the PC crap, you will eventually come to a single, important truth: sexuality is way too complex to be solely the result of any single magic bullet. Perhaps more importantly is that children are not born sexually mature, and hence the idea that they are born homosexual is as ridiculoius as the notion that they are born heterosexual. They are born asexual in that they are not yet sexually mature.
It is PC to say that there is genetic determinism that makes a person be gay due to hard-wired mental functions from the genes. This is absurd, because the "hard wires" of the brain aren't really that hard at all. The brain in a newborn has many, many more synaptic connections than needed. Throughout life, as we learn and develop more fully, these synapses are reduced in some places and increased in others. The experiences of life, along with things like diet, make the brain develop as it does in complicated ways.
The fundamentalist tends to say that the matter is purely a matter of choice. This is equally absurd. While it is correct to say that a person is responsible for their actions, the desires, thoughts, and emoptions of the brain are not so easily controlled. The brain does eventually wire itself in certain ways and it does lose flexibility as time progresses. But the results are not purely choice.
The answer is somewhere in between. There are differences in people's genetic makeup and developmental processes that make some people more strongly predisposed to certain sexual tendencies, I'd expect. But the experiences of life will always effect the ways in which the genes are expressed, and this is unavoidable. Monozygotic twins have the exact same DNA as one another. If one is a hemophylliac, the other one will also be, with absolute certainty. The correlations for sexuality, though strong, are not 1:1 like this. So there ahs to be something more than genes. No one can positively identify what particular environmental cues or experiences or hormonal cascades are necessary for a given line of developing a particular sexuality, but the fact that we haven't elucidated the path does not in any way mean the path does not exist.