1. In the US, perhaps, but here marriage has always been regulated by federal law, under the Marriage Act 1961 (changed a few times, since then!) and our Constitution.
2. "Actually, western civilization and America have honored the definition of marriage as being the
union of one man and one woman for centuries. America has known no other definition." That a cute appeal to tradition, argumentum ad antiquatum, but slavery was also practiced for centuries - hardly makes it a good thing. Also, I think that some Native Americans tribes had polygamy, and they certainly had the Two-Spirits, who often married same-sex partners.
3. Benefits for the nation, meaning children? Well, some gay people can and do have children, lesbian couples I know, and you don't know what those kids will do for a future career.
4. "Again, America has never acknowledged any other definition of marriage and we need not change this time honored institution to conform to the whims of a small minority of loud people." White America, you mean? Well, as I have already pointed out, Native Americans acknowledged other forms of marriage.
5. "Gays can have their rights and dignity without us changing the definition of marriage. They can have their relationships if they wish. They just can't call it marriage." Replace the "gays" in that sentence with "blacks" - or any other race or nationality. Then, that's how you sounds to a LOT of more tolerant people.
6. "Genetically, there is no evidence that homosexuality is genetic." A lot of things have not been proven to be genetic, does that mean we should outlaw them. "Actually, before gays organized and formed a powerful lobby, homosexuality was a diagnosable mental illness as per psychology and psychiatry." Yes, and a 'schizophrenic' used to mean someone with split personalities, now called MPD, psychiatry changes things over time. The reason a lot of homosexuals used to plead insanity, back when it was still illegal, was the same reason that murderers still do, this meant a more cushy sentence for them. They were better off taking to the streets - at Stonewall and elsewhere.
7. Ah, you people always have a slippery slope...get your skis! PIB (i.e. polygamy, incest, bestiality), as John Corvino calls it, are all still illegal, in most countries that have SSM. However, polygamy is legal in many Middle Eastern countries, where homosexuality is still illegal.
8. We are all Homo Sapiens, however the sapience is doubtful, in your case. Who cares what you support? We're talking people's private lives, here, not a sporting match, for all the football, basketball or cricket supporters to turn up.
There you go, refuting your arguments was a piece of cake, wedding cake that is, with two Ken dolls as grooms on top! That's the reason SSM has spread to most Western countries, because there are no real arguments against it. Finally, I never called you any names, but telling people they suck, makes you sounds like a self-loathing closet case (I think you'd like to, Ziggy Freud).