It isn't their behaviors that are at issue. It's the re-defining of marriage as between any two people --regardless of sex. It's an absurdity we never thought possible when I was growing up.
Homosexual behaviors have always been with us --just like adultery, pedophilia, pre-marital sex and pregnancy, sex-slavery, incest, rape, bigamy, polygamy, the desire to transgender, transvestitism, prostitution, porn --and a very few "shacked up" without marriage. There really used to be a lot of shame on losing virginity and pre-marital pregnancy and living together "without benefit of clergy," which is how they described "shacking up." Most rare of all in American society, I trust, was bestiality. All of these are forbidden in the Bible and many have been frowned upon and discouraged in every HUMANE civilization and culture since the dawn of time. Wherever these behaviors were prevalent, the culture has not been admired by history today.
None of these other deviations from the preferred ideal of hetero-marriage have sponsored pride parades in America or asked for legal sanction through the institution called "marriage."
Why should hetero marriage be favored? Simple. It's the institution that brings children into the world with a father and mother who are married to each other, stay together to be the grandparents together, provide male and female role modeling for their sons and daughters. Hetero marriage provides a stable, emotional and economic support system in which to bear, raise, nurture, protect, supervise and educate the next generation. Thus, we will have a future --future military and workers and family members to support the older generations --future married parents to bring on the future generations.
Homosexual relationships are comparatively the end of the road --they don't make children and just don't need the perks of the hetero married who volunteer to take on the burdens of bearing and rearing kids. If they have kids, they didn't make them as a gay couple. There is a father in the case of lesbian parents who needs to pay child support. When two men adopt a child, they both work and afford a nanny. And that mother figure typically changes through the years. The child truly has no mother.
We are crazy to tamper with the definition of marriage to include people of the same sex.
"God is not willing that any should perish, but that all should come to repentance and have eternal life."--the Bible