Here’s one of the main arguments (pdf) of Paul Clement, who is defending DOMA before the Supreme Court:

It is no exaggeration to say that the institution of marriage was a direct response to the unique tendency of opposite-sex relationships to produce unplanned and unintended offspring. Although much has changed over the years, the biological fact that opposite-sex relationships have a unique tendency to produce unplanned and unintended offspring has not.  While medical advances, and the amendment of adoption laws through the democratic process, have made it possible for same-sex couples to raise children, substantial advance planning is required. Only opposite-sex relationships have the tendency to produce children without such advance planning (indeed, especially without advance planning).

Weigel raises an eyebrow:

[O]ne of the ways gay couples find children to raise is by adopting them — adopting children who are the unintended product of opposite-sex relationships. In all seriousness, did no one proofread this?

Chait further unpacks the illogic:

[T]he problem here is that you can’t discriminate against people without good cause. You need some distinction to justify it. The traditional distinction that straight people raise kids doesn’t work, since gay couples can do that too. So Clement fell back on arguing that only straight couples have unplanned children. Gay couples don’t get drunk and wake up pregnant. It is, to say the least, ironic that after years of using alleged gay social irresponsibility as a rationale for discrimination against gays, heterosexual irresponsibility is now a rationale for discrimination against gays.

And it’s all they’ve now got: keep gays out of marriage because straights can get knocked up accidentally (and for some reason need an exclusive institution to keep up appearances). But I still fail to see how gays’ ability to get married somehow reduces the availability of straight shotgun marriages. There just isn’t a trade-off here. It’s win-win: for marriage, for gays and for straights.Unless you are working from a premise that gays are icky and their very inclusion in civil marriage inherently debases it.

Which is why David Blankenhorn’s new venture is so worth supporting. It gets us out of the gay-straight division and back to the real question: how civil marriage can help a society rear children more effectively and foster more responsible and happy adults. If you’re a conservative who believes this helps society stay stable, you will, like Blankenhorn, at some point leave the focus on what you’re against to regain the focus on what you are for.