And yet strangely they don't insist that LGBQ's are bigots if they refuse to date hetero. How curious :-/

The eventual goal of dating is sex. Perhaps not in an immediate sense, but eventually.
I'm fat.
Some people are attracted to fat people.
Some aren't.
If you don't find me attractive, you shouldn't date me. You are setting it up to either break up with me, or to have sex with someone you're not attracted to.
As long as you aren't overly harsh about it, you can (and should) turn down advances from people you know you never want to have sex with, regardless of the reason you're not attracted to them.
It's not bigotry (against fat people or trans persons), it's an acknowledgement that a romantic relationship cannot progress to the final (or even a critical) point, due to personal preferences.

I don't think you understand how being gay works cr01