I think that starts from not quoting/supporting people who are known for being bigoted in defence of your views.
"Denying the existence of two sexes is to deny the existence of homosexuality"
This doesn't make sense to me.
If I believe there are several genders and sex is irrelevant, I can still believe that men exist who are only attracted to men. It's just that who I define as men might be broader than someone who doesn't subscribe to gender ideology.
Similarly, I can believe that there are several genders and that sex is irrelevant, and still believe that some men are only attracted to biological men.
So I can't see a way where denial that there are only there are only two sexes automatically denies the existence of homosexuality.