A recent, and interesting, development in the legal world is the conversion (?--I don't know what he believed in the first place) of Ted Olson, former Bush 43 solicitor general and conservative legal scholar par excellence, to the pro-gay marriage camp. He details his thoughts on the constitutionality of same-sex marriage, based on the 14th Amendment's guarantees to "the equal protection of the laws" and "due process of law."
Now, I have to say that I honestly don't know what I think about civil same-sex marriage. From a religious point of view, I don't believe homosexual acts to be morally right. But something being morally wrong or distasteful doesn't necessarily mean that it is or should be legally unacceptable (see, e.g., hate speech protected by the First Amendment). However, I find Mr. Olson's reasoning to be lacking.
His argument, which is the one usually heard, is that allowing heterosexual marriage but not homosexual marriage means that we are treating homosexuals unequally. That simply depends on how you view it; society has granted the right of a man to marry a woman and a woman to marry a man. A homosexual man can marry a woman, just as a heterosexual man can. They are treated the exact same. Now, the fact that the gay man doesn't want to marry a woman doesn't change the fact that they are treated equally under the law. Of course, if you view it through the prism of "a man loves a woman, he can marry her so a man loves a man, he should be able to marry him," then you'll disagree with my reasoning. That would make 'homosexuals' a new protected class, which is something those who appreciate individual rights eschew. I guess it depends on what the courts feel. My point, though, is that the 'equal protection' argument is not so cut-and-dry as Olson suggests.
Now, he is correct that most conservative reasoning against gay marriage is bad. It'll hurt heterosexual marriage? Please. No procreation?? Tons of people get married and never intend to have children. "Tradition"? Traditions have changed throughout history and continue to do so. It's legitimate to argue that this one shouldn't, but then, the obvious question is "why?" which leads us back to the other, less-than-convincing reasonings.
He is wrong on some of his arguments, too--that 'science' has told us gay people are naturally, instead of 'nurturally' homosexual, and therefore it should be societally accepted (children of alcoholics are predisposed to alcoholism, but that doesn't excuse any DUI's they get, so natural proclivity to a behavior does not result in appropriateness of legality) or that supporting loving relationships of any kind should be celebrated as an 'American value' (would Mr. Olson believe that polyamory should be legally recognized? Likely not, though his argument taken to its logical conclusion would say so).
My biggest concern, however, is timing. Something that litigators constantly seem to forget is the democratic process. You see, it's the people who should determine the meaning of the Constitution. That is exactly how the Eighth Amendment--against "cruel and unusual punishment"--is interpreted. What is cruel or unusual depends on what society believes is cruel and unusual. Similarly, the definition of marriage--and whether 'equality' applies--should be determined by the people. 39 states have now determined, through the referendum process, that marriage is a union between a man and a woman. To treat that determination as akin to southern racists making interracial marriage illegal as Mr. Olson does is rather over-the-top. Even if he's right and history is on his side, perhaps he should wait until the people are more accepting, as they were when the Supreme Court disallowed bans on interracial marriage (yes, yes, many southerners were up-in-arms, but the public tide was obviously against them). Not that that would make same-sex marriage any more or less constitutional, but it would certainly tone down the culture wars, which have largely been caused by the Supreme Court's creation of social policy (anyone who thinks Roe v. Wade solved anything is crazy; it only created our society's abortion obsession, largely because the Court's ruling so offended the mainstream of America).
I think that Mr. Olson's argument is flawed. Not fatally, but certainly to a point that he should address. This issue is not as simple and obvious as he acts. Beyond that, even if he wins, the timing and venue are poor. If he wants to say that the gay couples he knows are fine, upstanding citizens, then his battleground isn't the federal court system but the streets of America, to convince his fellow citizens. The Courts are a cheap and divisive place to do battle. Were the Supreme Court to determine that same-sex marriage is a constitutional right--without even a pretense that it's what the founders or the writers of the 14th Amendment meant--it would simply engender more distrust in government, anger at the subjugation of the democratic process, and resentment that the Supreme Court would have the audacity to spit in the eye of the public's clear wishes. That's not how the institution (or the Constitution) should work.
UPDATE: Obviously, I'm not the only one saying things about this. Apparently, the gay community is not particularly excited about the efforts Mr. Olson and Mr. Boies are making, since they feel it will do more harm than good to the gay rights movement to push it through the courts like this. See the Slate article on that here (also, be aware that the article was written before the Supreme Court ordered that the hearings not be broadcast, so there will be no YouTube presence).
UPDATE II: Ted Olson's opening statement, as prepared.