Whether you like it or not, the guys who watch it are straight. They are only attracted to women and they only want sex with a woman. You may think they are gay but they don't think so nor do the scientists who research this issue. Guys who watch shemale porn never watch gay porn bu they do watch straight porn. Now why is that?
Call it what you want but there is no way on earth you're straight if you're watching shemale porn fantasising about fucking a shemale, sucking cock, or getting fucked in your ass.
There are all variations of people with mixtures of chromosomes. Some people grow up thinking they are biological women and until they try to have children, only then do they discover they have XY chromosomes. There is a lot more involved than that to make someone a man or a woman. You need to do some reading on current scientific research into gender.