Are you sure genetics have absolutely no role in behavior? Has this been proven? The meat analogy isn't quite convincing me.
To me, intersex explains a lot. Intersex are born this way, so why can't gays be born this way? Why can't CDs be born this way? We can choose not to be what we really are I guess.
It may be nurture rather than nature, idk. There isn't enough evidence for me to speak in absolutes one way or the other. Most of us are conveying our experience in this thread of why, and we're all a little different (unique). That ain't scientific though. Most of us had early childhood CD experiences that returned big time at adolescence, but genetics might also be involved. Humans are quite complex which has me keeping an open mind on this topic.