A biblical definition of marriage

“Bible-believing” Christians desperately want gay marriage to be illegal. They say it’s because that’s what the Bible teaches.

However, in the New Testament Jesus says remarriage after divorce is a sin, but I don’t see Christians fighting to make that illegal. And Paul explicitly forbids marriage between Christians and non-Christians, but I don’t see Christians trying to criminalize inter-religious marriage.

So, what’s with the cherry-picking, Christians? Why can’t you be consistent?