Christians have scripture that homosexuality is an “Abomination” in the eyes of God; case closed.
Sick and immoral behavior.
...and “abomination” means “abhorrent, disgusting, stinking.”
In reality, their beef is with God, and their objections will only result in worse punishment. God has already judged homosexuality, and all unrepentant homosexuals will go to hell and the lake of fire. They’re insanely trading a few years of righteousness here on earth for an eternity of absolutely merciless torture, and it’s God who’ll do the torturing.