Rush Limbaugh says that the left won the gay marriage debate when they successfully changed the definition of "marriage":
We Lost Once We Modified the Definition of the Word "Marriage"
The language game, the left really excels at changing the language to benefit them politically, and they do it in such a way that a lot of people on our side have no idea what's happened until it's too late and the issue is already lost, which this issue is. This issue is lost. I don't care what the Supreme Court does, this is now inevitable -- and it's inevitable because we lost the language on this.
The left won but I am not sure who the "we" is that lost. I am familiar with other conservatives who seemed to have no problem with gay marriage as long as it arrived by way of the legislative process rather than judicial cram-down. Justice Kennedy seems to be looking for a way to sidestep his own logic and let the shift in public opinion in favor of gay rights run its course.
Ann Althouse makes the point that other than the conventional definition of marriage, gay marriage opponents were a bit short of coherent arguments. Religious disapproval doesn't qualify in our secular state; moral disapproval was cast aside with Lawrence v. Texas.
And there is the concern that homophobic hyper-macho young men already disinclined to marry the young women they are impregnating will be even less inclined if marriage is re-branded as a "gay thing". But pandering to homophobes is a pretty weak foundation for social policy, and perhaps the broad change in attitude will sweep that away.