So, in other words, you could choose to have gay sex.
If you mean that as me, personally, except for a few very, very good drag queens, I've never been attracted to a man. And then, the attraction was that they looked like really good looking women. (BTW, I've never acted on such an attraction.)
If you mean do people, in general choose to have gay sex, except for rape, everyone who has sex makes a choice to do so. However, I do believe that at least some gay people cannot help being gay.
The question is, if two people of the same sex are attracted to each other -- something that they can't help -- should they be expected to resist acting on that attraction -- something that they can help?
But even that doesn't apply only to gays. I'm a married man, who believes in being faithful. Therefore, even if am attracted to a woman, I would not pursue having sex with her (unless, by some wild chance, my wife told me to).