Theodore Olson has entered the fray over Virginia's ban on gay marriage. Olson, a powerhouse Republican lawyer who helped keep Al Gore out of the White House, is joining forces with the ACLU (which is challenging the ban in a separate suit) and what those on the right like to call the "homosexual lobby." This adds a big wrinkle to the standard left/right narrative, and raises a question: Is there a conservative case for gay marriage?

There certainly is a liberal one: Diversity is great, which means gay people are great – so if they want to marry, that's great too! Besides, you're not supposed to discriminate against anybody. (Except conservative Christians, because they're so judgmental and icky.)

There is also a libertarian argument for gay marriage, which is equally straightforward: Short of actually shooting somebody in the face, individuals should be able to do pretty much whatever they want (except criticize the novels of Ayn Rand, no matter how hilariously bad her prose). If that means two burly lumberjacks get to pick out china patterns together – hey, go for it.

Most everyone also knows the conservative argument against gay marriage: God made Adam and Eve, not Adam and Steve. Plus, look at these pictures from the San Francisco gay-pride parade we found on the Internet. Dude, are you seriously gonna stand up for those freaks?

Olson has. With Democratic lawyer David Boies, he successfully challenged California's ban on gay marriage. In 2010, Olson penned a piece for Newsweek explaining his version of "The Conservative Case for Gay Marriage." He pointed out that "same-sex unions promote the values conservatives prize" – such as commitment, stable families, and "thinking beyond one's own needs." Moreover, gay marriage follows from the "bedrock American principle of equality." If you believe in the values of the Declaration and the Constitution, then you believe in equal rights, and "marriage is one of the most fundamental rights that we have as Americans."

Those are good reasons. But they are not the only reasons conservatives might accept gay marriage. Here are five more.

(1) Gay marriage is good for "the institution of marriage."

If you think marriage is a valuable cultural institution, and you worry about its decline in contemporary America, then you should welcome a reform that would shore up that institution against erosion. Just as the institution of banking is stronger with many participants rather than few, having more marriages rather than fewer is better for the institution of marriage.

Granted, you can push this argument too far. The institution of marriage would not be strengthened by "marriages" joining, say, cats and mice in holy matrimony. But those unions do not entail any intent to participate in the institution; cats and mice are not buying in to any set of values when people pretend to marry them off. When gay people seek to marry, however, they do intend to participate in marriage, and they do buy in to a (conservative) value set.

(2) Gay marriage fosters virtue.

Social conservatives believe sexual promiscuity is bad for the body and corrosive to the soul – that the sexual revolution's encouragement of licentiousness has degraded social norms and debased our common virtue. If they are right about that, then allowing homosexuals to enter lifetime monogamy ought to be altogether desirable – just as it is desirable for heterosexuals, and for the same reasons.

(3) Gay marriage benefits children.

In his 2012 book A Fundamental Freedom: Why Republicans, Conservatives, and Libertarians Should Support Gay Rights, David Lampo notes that "over a quarter of a million children are living with same-sex couples." Forbidding those couples to marry does not spirit their children away from them into the arms of straight couples (which likely would be awful for those children anyway). All it does, as the ACLU points out, is deny those children "the protection and stability of having parents who are married."

But how do those children fare compared with children raised by straight couples? "There is no evidence that gay parents are any less effective or loving than heterosexual ones," Lampo writes. In fact, some studies (such as one conducted by the University of Melbourne) show children raised by gay couples are better off by some measures (e.g., family cohesion) and no worse off in others (e.g., self-esteem). According to the Supreme Court, voluminous research indicates that children raised by gay or lesbian couples "are as likely as children raised by heterosexual parents to be healthy, successful and well-adjusted."

(4) Banning gay marriage injects government where it doesn't belong.

Conservatives probably will respond to the previous point by contending that while letting single-gender couples raise children might not be profoundly harmful, it certainly is not optimal. The optimal family, they will say, consists of children raised by two parents of the opposite sex.

Let's accept this as true for argument's sake. But while it is one thing to stipulate what might be optimal, it is something else – something far more dangerous – to suggest the state should impose its view of what is optimal on the nation's families.

After all, the optimal conditions for child-rearing extend far beyond parental gender. We can easily imagine what a government in the hands of left-wing activists might consider optimal: No guns in the home. No smoking, either. Certainly no spanking. And absolutely, positively no trying to cure a sick child with prayer.

In fact, a government that was to impose its view of optimal child-rearing conditions would not start by forbidding gay couples to marry, since their marital status has nothing to do with their child-rearing skills. Rather, a government bent on optimal parenting, as conservatives define it, would start by banning divorce. (And to be fair, some conservatives – such as Virginia gubernatorial candidate Ken Cuccinelli – do want to make divorcing more difficult.) Having banned divorce, social conservatives trying to optimize parenting would then take children from single-parent homes, where they face much longer odds of life success, and require two-parent families to adopt them.

(5) Banning gay marriage encourages big-government thinking.

Conservatives content they want to protect the institution of marriage and foster procreation by straight couples. First question: Show me where the Constitution says that is any part of government's job. Go ahead, I'll wait.

Can't find it, can you? Even if someone could, the means chosen – banning gay marriage – is connected to those goals only by logic so thin and weak it cannot stand up. Letting gay people marry does not discourage straight people from getting married, and it certainly does not discourage them from procreating. (What spouse has ever said, "Gee, honey, I'd love too, but not tonight – seeing Kevin and Don's engagement announcement kind of spoiled the mood"?) Gay marriage simply has nothing to do with either of those issues.

By pretending it does, conservatives adopt precisely the sort of big-government thinking they otherwise abhor. If government is supposed to encourage procreation, then the law should be narrowly tailored to achieve that goal. (For instance, straight couples seeking to marry should have to take fertility tests.) By suggesting government can exclude gays from marriage in order to encourage procreation, even though the two issues have no relation to each other, conservatives encourage government to claim it can do anything at all so long as it has what James Madison called a "colorable pretext" for its actions. That's exactly the kind of thinking that led to Kelo, the Supreme Court decision allowing local governments to confiscate private property if they think they might one day find a better use for it.

Finally, conservative say the traditional straight family is – well, traditional. But as another court has noted, this does not explain the reason for discriminating against gays, it merely repeats it.

Repeating a conclusion doesn't prove it. And besides: "Upholding tradition" doesn't appear anywhere in the Constitution, either.