"When a heterosexual act is committed, even in fornication or adultery, the act itself conforms to the way God created man and women."
This is true, and adds to homosexuality yet another layer of depravity.
But I would note that when heterosexuals contracept, the act no longer conforms to the way God created men and women. It is an active and intentional rejection of God's design as inscribed in the body.
Contraception and sterilization are similar, as well, to the sex-change project: transsexualism. They involve using drugs, devices, and surgery to change the normal, natural, functional body into something which is abnormal, unnatural and dysfunctional in the sense of being procreatively disabled.
Contraception, transsexualism and homosexuality are all way over on the spectrum of rebellion against the way God created our bodies.
I don’t think Western culture would even be entertaining the idea of redefining marriage now if Protestantism hadn’t started caving into the pro-birth control mentality such as the Anglicans did circa 1930. Actions and ideas have all sorts of consequences(intended and unintended both) to ripple through many generations.