Or the Edo-era Japanese. Or the pre-Christian Romans. Or, I'm sure, lots more examples I'm unaware of that existed before exposure to Judeo-Christian doctrine. Though he claims the argument is secular, it presupposes the "correctness" of Anglo-American norms which, hey, lookit that, are heavily grounded in Protestant, Puritan traditions.
Calling some of the violence experienced by homosexuals as "occasional slights" is pretty damn offensive as well, and someone needs to point that asshole in the direction of Mathew Sheppard and other similar cases.
And, really, I want to fucking slap everybody who makes the claim "NO WE CAN'T REDEFINE MARRIAGE BECAUSE THEN WE CAN REDEFINE IT HOWEVER WE WANT." Do some fucking homework; Christian marriage has changed a lot over history--it wasn't even considered a holy sacrament until the Gregorian reform in the 13th century, and the Protestant Reformation (and the accompanying Counter-Reformation) changed it quite a bit as well, though I know a little less about the specifics of those changes. People have been redefining marriage for centuries, and just like the rest of his pathetic little argument, this assertion is based on ignorance and unfounded presupposition. If you're going to argue, do your homework, otherwise (at the risk of sounding like Bill O'Reilly...) shut the fuck up.