Why is the assumption so often made that marriage is a Christian tradition?

It's because people are lacking knowledge. Marriage did NOT start in Christianity. Infact, it didn't even start in Judaism! Ancient cultures were marrying people, before religions were even around! The whole point of marriage is that you are tied together with that special someone forever.

Marriage has nothing to do with religion.

You get married in the courts and sign your marriage contract, you are married legally.

If all you do is have a ceremony in a church, you are not legally married!

If marriage is solely christian and that is why they say gays can't marry, then they must also not allow other religions to marry, a couple with two different religions, inter-racial, old people, infertile couples, and basically ban EVERYONE from marriage except christians.

**"Thank God I'm From Texas"- Using your logic, then you must also say that since Santa is very deeply rooted into Christmas, that Santa therefore created the Christmas holiday. Or that the Easter Bunny started Easter. Aka- You don't make sense.

(Leviticus 18:22) “Thou shalt not lie with mankind, as with womankind: it is abomination.” Scripturally lawfully the government has no right to tell a true church who they can and can not endorse as a candidate. No true Christian should have voted for Mr. Oboma. He is a baby butcher. He said "the first thing I'd do is sign the freedom of choice act." This would allow partial birth abortion and the execution of a baby born perfectly alive after a failed abortion. A church must warn people of these things because they offend a holy God. They are sin. All have sinned, and come short of the glory of God. The wages of sin is death. And death and hell shall be cast into the lake of fire. God does loves us both you and I (Luke 13:5) but, except ye repent, ye shall all likewise perish. We do not preach against same sex marriage because the state lets us but because God commands us. You are right in that marriage did not begin with Christians, but it did begin with God. There for (Hebrews 13:4) Marriage is honourable in all, and the bed undefiled: but whoremongers and adulterers God will judge.

I think it only because Christianity is a majority in America.

Because if the same thing happened in Indonesia, a predominantly Muslim country, I guess the assumption would be that it is an Islamic tradition.

So, I think those are just coincidence. It's human nature to act that way.

Well "marriage" is pretty deeply rooted in religious values, so it's hard to shake that from people's minds nowadays. Proposition 8 wasn't a church proposition, it was strictly a political process. It just so happened that the people, including Christians, are the ones who voted on this and the majority just so happened to have won.