(Once I even put that title down, it carries a very strong implication: I could only "choose" to be heterosexual if I were not, already, such. Only a gay person could "choose" heterosexuality, then.
So this post is really how my heterosexuality developed, as best as I remember it.) When I was a young boy, four or five, I took comfort in these tiny imaginary female figures who would dance around in my lap before I went to sleep. Their explicit origin, as I far as I can determine, was Tinker Bell, from the Disney movie "Peter Pan." I had some wooden blocks with figures from this movie on them, and also a record album with an illustrated booklet, based on that movie. These figures, at one point, became sexualized. I must have been about 10. At some point, instead of being small, they became life sized, because it was awkward kissing such small fairies. One night, I had a sudden, jerking, "accidental" discharge while fantasizing about them. I had no idea what is was, because that was explained to me in sex education a year after that. A year too late for me to have been helped.
The original fairy-like creatures were subsequently replaced by images of actresses, or other adult women I could visualize. Since I was 10, I didn't fantasize about 10-year old girls. In fact, I had crushes on girls my age but didn't really think about them sexually, because they just didn't coincide with my desires (yet). [I no longer care much for Tinker Bell, and you might think it's a stupid way to become heterosexual, but in my defense I must say that I was a tiny kid when I started to fall for her.]
And that is how I "chose" heterosexuality. I actually didn't know I had a choice, because the objects of my fantasy were already there, present in my lap from the time I was four. When they came to life, suddenly one night, as a different sort of figure, I had no idea that I could have "chosen" an equivalent set of male figures.
This is why every heterosexual man actually knows that gay men do not choose a "lifestyle"* of being attracted to other men. Just ask the question: when did you choose between men and women as the object of your desire? If my story is at all typical (not in details, but in its general drift) then you never really made a choice. The sexual object was already there, probably, before it was even sexualized (in the conscious mind).
Another strong element in resistance to homosexuality is the idea that heterosexuality is this enormously fragile thing, that must be sustained by endless football games, gallons of lipstick, and socially sanctioned bullying. (Every boy who was small and bad at sports, as I was, was called a faggot all the time. You didn't actually have to be gay to get this treatment.) Really, though, it not so delicate a creature. It will do fine, really. Don't worry. People who worry that "if everyone is gay, then how can the species survive" seem rather comical to me, given the size of the world population and the relatively robust nature of heterosexuality.
*By "lifestyle" (stupid word for this) people apparently mean living as a gay person, if you are gay. But I could live a thousand different lifestyle, Bohemian, bourgeois, communal, monastic, military, rural, etc... and I would still have the same sexual desires and preferences.