To expand on what Eki is saying,
Christianity, Islam, whatever, pretty much all the major religions
They all carry heavy messages of love and tolerance. In literally every major religion, you will find some variation of "The Golden Rule", Do unto others as you would have done on yourself.
Contradictory to this are a few passages in the bible, and I'm sure in some other religious texts, that denounce homosexuality, inter-racial marriage, People of different ethnicity/creed, etc. as abomination. But, as
Dan savage so inappropriately said at a journalism convention quite recently, Christians have learned to ignore the bull **** in the bible
And it all stems from how the religion has evolved, becoming more and more progressive as society marches on. Social issues that were once taboo are now discussed and becoming accepted. As the western culture becomes more accepting of different things, so do the beliefs of the people (sorry for focusing on Christianity, the Bible is the only religious text I've read any of)
So in this progressed religion, we see some people who still have an issue with gay marriage. Why?
Well, to understand why you have to ignore the religious aspect. its a RUSE.........
These people dislike gays, and will justify it any way they can. If the bible said "God is a-okay with gay people" these people wouldn't care, they would cite some other text that demonizes homosexuals
To provide an anecdote, a friend of mine recently confided in me "I'm depressed because of existentialism"
He said to me, "If everything is pointless what's the point in being happy"
And I responded simply: "Well then what's the point in being sad"
This is what I'm getting at, when you can use these peoples logic against them, they don't actually subscribe to that logic
Just as my friends depression didn't stem from existentialism, and instead the existentialism stemmed from depression
These "Christians" have bigotry that doesn't actually stem from mainstream christianity, Their brand of it stems from their bigotry
That's why you can say "well the bible is also radically pro-slavery" against them