Sure, that's true enough.
But as a straight guy, I wouldn't want to have sex with another dude. The idea of sticking my dick in his butthole (or his in mine) isn't something I would look forward to. To get it hard I would have to think about stuff I like.
If I much rather would want to have a woman and a her vagina to stick my dick in, that would make me a straight guy, right? It's what make me aroused and bisexual people don't care which it is. They can get it on with both.