I'm not so sure about that. I am a male who happens to be sexually attracted to women. I have never felt sexually attracted to men. I did not make a choice to be this way. It does not require any willpower on my part to avoid having sex with men. Likewise there appear to be some people who are indeed sexually attracted to the same sex or to both sexes. It is likely that they did not "choose" to be this way either. It seems to me that many people who say that sexual preference is a choice probably feel sexual attraction to both sexes and must use willpower to fight the attraction to their own sex.
And not one of my gay friends would agree with you. Every one of them laughed at the idea that being gay was genetic. ("Yeah. I got the gay gene from the man who had sex with my mother... riiiight.") They all told me that they had terrible, traumatic childhoods. Some of them were just deeply neglected or felt outcast and were looking for a place to belong. Being gay is a combination of sex and a twisted mental development.
Better than being a serial killer or into a fire thing...