Well, remembering my stance from evangelical days, I think the train of thought went something like this…
1.) Heterosexuals do NOT choose because God made them that way.
2.) Homosexuals DO choose because they’ve been influenced by ________ (fill in the blank with environment, someone ‘converted’ them, they hate women/men, they were raped, and on and on ad naseum) and since the Old Testament declares the sexual act for them to be a sin, then if they absolutely have to stay that way due to circumstances, then God can deliver them by allowing them to remain abstinent or making them ‘straight.’ (See all the debunking and hype about so-called “Ex Gay” ministries. It’s incredibly eye opening.)
3.) Hi, Opal! <---- I’ve always wanted to do that, but don’t think I ever had. 
4.) That’s about the only rational there is and most don’t give it any thought beyond that (and it’s icky, wrong, “unnatural,” immoral, yadda, yadda, yadda) and it destroying everything. I’m sure you know the many claims that it was behind the 9/11 attacks, it’s God’s punishment via AIDS, that was the fall of Rome.
And you know, back in the day, no one ever suggested to me to try the reverse theory. I never went, “Well, duh! I didn’t choose to be straight, it just happened. Therefore, it must be the same way for them!!” or realized that no one would just decide such a difficult life, where they’re very humanity is questioned, they can be beat or murdered for no other reason than their orientation or they’re simply made to be social outcasts, pariahs or even third class citizens. Amazing that doesn’t come up more often (or at all). I can’t imagine how hard it must be to keep going, hold your head high and focus on the positive if people think you’re evil, don’t deserve to live, will molest their children and burn in hell. My heart continually goes out to them.
Hope that helps, from at least one former fundamentalist’s perspective.