Here's Steve King (W-IA), explaining why the gays shouldn't be able to marry.
Marriage is the stable platform from which families are launched. Government surely has a compelling interest in ensuring the stability of that platform, and even subsidizing the practice with tax incentives. Moreover, society has an interest in promoting procreation amongst married adults. Same-sex marriage does not present the possibility of natural procreation nor has same-sex parenting endured and thrived for millennia of human experience.
Does King think the government should outlaw divorce, since that would certainly "ensure the stability" of marriage? Does he think the government should bar people over 50 from marrying, since they can't naturally procreate? I'm guessing no.
Insisting upon heterosexual marriage is therefore not discriminatory, nor does it constitute the government telling anyone whom to love. The argument for upholding the Defense of Marriage Act is rooted in the way marriage is historically treated by state laws. To understand why government is involved in marriage in the first place is to understand why government cannot validate same-sex marriage.
Very small government-y!
Nice to see that the wingers at The National Review, which published impassioned defenses of Jim Crow (by Buckley!), are honoring their traditions.