NRO has an excellent piece on the subject.
Maggie’s Top Eight Reasons Why Gay Marriage Is Not Inevitable
1. Nothing is inevitable.
We are talking about the future here. It’s weird to have “reporting” that something that has not yet happened will certainly happen. The future is never inevitable.
2. Young people are not as unanimous as most people think.
In California, the young-adults vote split 55 percent to 45 percent. Is it so hard to imagine 5 percent of those young people changing their minds as they move through the life cycle?
3. The argument from despair is bait and switch.
They are trying push the idea that gay marriage is inevitable, because they are losing the argument that gay marriage is a good idea.
4. Progressives are often wrong about the future.
Here’s my personal litany: Progressives told me abortion would be a dead issue by today, because young people in 1975 were so pro-choice. They told me there would be no more homemakers at all by the year 2000, because of the attitudes and values of young women in 1975. Some even told me the Soviet Union was the wave of the future. I mean, really, fool me once shame on you. Fool me over and over again . . . I must be a Republican!
5. Demography could be destiny.
If there is one force that directly contradicts the inevitability argument, it is that traditionalists have more children. Preventing schools and media from corrupting those children is a problem, but not necessarily an insoluable one. Religous groups are increasingly focused on the problem of how to transmit a marriage culture to the next generation (see the USCCB’s recent initiatives).
6. Change is inevitable.
Generational arguments tend to work only for one generation: Right now, it’s “cool” to be pro-gay marriage. In ten years, it will be what the old folks think. Even gay people may decide, as they get used to living in a tolerant and free America, they don’t want to waste all that time and energy on a symbolic social issue, anyway. (I know gay people who think that right now). I am not saying it will happen, only that it could. The future is not going to look like the present (see point one above). Inevitability is a manufactured narrative, not a fundamental truth.
7. Newsflash: 18-year-olds can be wrong.
Should we really say “Hmm, whatever the 18-year-olds think, that must be inevitable,” and go do that? I mean, would we reason like that on any other issue?
8. New York’s highest court was right.
From Hernandez v. Robles:
The dissenters assert confidently that “future generations” will agree with their view of this case (dissenting op at 396). We do not predict what people will think generations from now, but we believe the present generation should have a chance to decide the issue through its elected representatives. We therefore express our hope that the participants in the controversy over same-sex marriage will address their arguments to the Legislature; that the Legislature will listen and decide as wisely as it can; and that those unhappy with the result — as many undoubtedly will be — will respect it as people in a democratic state should respect choices democratically made.