I don't wish to comment on the science of this issue, but I will second the notion that "sexual orientation" can be and often is an issue of choice and psychological adaptation.
For example, people often times form fixations on certain fantasies that intrigue them sexually. Such fantasies can be as simple and "innocent" as colors, clothing and scents, or as "strange" and peculiar as pain, excrement, etc.
An individual I know, who has not ever considered himself "gay" or a "homosexual," engaged in all heterosexual relationships for many years. Then, suddenly, he entered into a homosexual relationship. At the time he found it exciting and interesting, but now finds it "disgusting" and repulsive. He cannot fully explain what happened to him or why, but he no longer has such attractions nor struggles with anything but memories of past events.
We cannot know the reasons why people turn out the way they do. Why does one person do one thing and another something entirely different? Nature/nurture debates continue to rage on. Regardless, we do not overly concern ourselves with the sources of our sins in this manner, but we concern ourselves with stamping them out for the glory of God.
Why spend excessive amounts of time debating where the concept of "stealing" comes from and why? We suffice it to say that it is wrong, and to stop it is what glorifies God. Likewise, the same is true of homosexual behaviors.
Most men struggle with pornography attraction for the majority of their lives. Do we rationalize this? Do we justify it? I would hope not. Instead, we seek better and more effective ways to fight it.
If the wolves are coming in and eating the sheep, what do you do? You build the best defenses you can to keep them out. Perhaps you even go on the offensive a little (and that's okay, since these wolves are hypothetical and for them to go extinct is good).
So build a defensive barrier around your life that sin has to look hard and long for the little cracks in your defense. And, when sin has found them, you must master it! For sin lurks at your door and waits to overpower you, but you must master it.