I think the problem isn't "gays". The problem is that most churches have already abandoned most of the constitutive elements of Biblical marriage.
According to Scripture, marriage is defined as man-woman (Genesis 2, referenced also by Jesus); lifelong (prophet Malachi says God "hates" divorce, Jesus says that a person who marries a divorced person is committing adultery); and procreative ("be fruitful and multiply"-- but implied by the very fact that they are malke and female: this is part of the natural "design".)
There is not a single instance of sexual partnering that is man-woman, lifelong, and procreative, that is condemned in he Bible. There is not a single instance of sexual partnering that is same-sex, non-lifelong, or anti-procreative, that is blessed in the Bible.
If I am in error here, please correct me.
But most "Christian" churches have already given up on 2 of 3, namely, lifelong and procreative. They OK divorce/remarriage and they OK anti-procreative acts, e.g. contracepted sex.
So most "Christian" churches have already re-defined marriage into a form contrary to what God has designed and defined.
Gays are just making it 3-out-of-3.
All because Henry XIII wanted a divorce and the Pope wouldn't grant it, so he started his own church. It's slid downhill from there.