Yes, they do choose their sexual orientation, just like fat people mostly choose to be fat by eating a lot. Fat people don't think, 'Hwy, I wanna be FAT!', no, they think, 'Man, those fudge brownies sure look good! Thinks I'll eat five, no one is looking.'
Homosexuals are a part of the 30ish percent that enjoy sex for reasons the majority of the rest of us do not. Those reasons vary from person to person, but a lot of it is having power over another person, or they enjoy humiliating or inflicting sexual pain on a person, or they just have this perverse enjoyment of doing what is forbidden by God and Nature.
The exact reason doesn't really matter, but this segment of the population drifts from the relatively mild philanderer like Bill Clinton, to bisexuality like Hillary to exclusive homosexuality that a small 2% engage in, and each of these people change from year to year through their whole lives.
There is no organ in you body that defines a person as homosexual; only behavior does that.
No, it is not bigotry to say that theft is a sin, and it is not bigotry to say that using ones sexual organs in a way that nature never intended is also a sin.