We don’t mistreat people for having disabilities
Except people do. Constantly. If people saw homosexuality as a physical disability, they'd get even more openly discriminated against instantly.
You think of oral sex as a paraphilia? Fuck, you must be boring. Sex is way more than missionary PIV with lights off for procreation only.
If homosexuality is a valid form of romance, why does nature deny them reproduction?
Reproduction isn't some kind of reward or evidence for a good romance, nor are romantic feelimgs required for succesfuö reproduction. It's a purely biological function, our feelings don't influence it at all.
Why do so few express interest in actually getting married, or treating it like the strict, closed relationship it is supposed to be?
Maybe because people are different and some know that a closed relationship isn't for them? How come so many straights treat marriage like a punishment, with shit like the Game Over marriage shirts, the ball-and-chain or cage imagery at weddings and the woman-dragging-man-to-the-altar cake toppers?