So someone made the claim that "LGBT people are heterophobic". They weren't listening to logic anyways, so why use logic, I just pointed out that some trans people are straight- and not all of the LGBT is heterophobic. They argued that trans sexuality (not to be confused with transsexuality) is based on assigned-sex, so trans people can't be straight. Let's ignore everything wrong with this statement. Here's my argument on why trans sexuality should be based on gender (if the person prefers it) more often than assigned-sex. I'm not going to get into "real" sex or surgery or anything like that. It pretty much comes down to this, for me.
The public part of a person's relationship is rarely sexual.
Okay, sure, sucking face can be considered sexual- but most people don't do that. They might talk about their sex lives, but that's their choice and not a requirement. It's completely acceptable for any couple to keep their intimate life private. If a mixed sex/gender couple enjoys the woman using a strap on on the man, no one needs to know. It doesn't make the relationship less straight. The parts involved, how they're used, and the positions they're used in aren't really relevant until you're at the point where sex is coming up.
Outside the bedroom (and inside the bedroom, but this is for those people who insist "No one can look at an assigned-male body and see a woman!")- most women want to be someone's girlfriend. This doesn't mean she wants to be submissive or take stereotypical "who wears the pants?" roles assigned to women, it means that she wants her partner(s) to see her as a woman. The relationship dynamic is at least partly based on her being accepted as the woman she is. Because of that- it makes more sense to define her sexuality by her gender, than by the genitalia she may or may not have.