On Tuesday, the U.S. Supreme Court will conduct a hearing on two cases  involving the question of whether same-sex couples have a constitutional right to marry. The Court might not reach this issue in either or both cases due to other legal issues in those cases. However, if the Court does rule on the issue of gay marriage, it should find that the Constitution does not provide such protection (although I predict that the Court actually will find gays to be a protected class for purposes of marriage, with Justice Kennedy casting the deciding vote alongside the four liberal justices). That said, as a conservative, I believe strongly that gay marriage should be legalized – by legislative action.
First, as a proponent of marriage equality, why would I oppose a ruling by the Supreme Court granting constitutional protection? The answer is that it is not within the Court’s constitutional powers to grant any right. The Court’s role is to interpret the Constitution based on the intent and understanding of the people at the time the constitutional provision at issue was ratified. There is no credible argument that any provision of the Constitution was ever intended to recognize or protect a right of homosexuals to marry. Marriage is, after all, an institution created by man and not nature or God (however much God may approve of the institution). Thus, if the Court properly interprets the Constitution based on original intent, it cannot justly find that the Constitution was intended to recognize or protect gay marriage.
Since it would be an abuse of power for the courts to declare marriage equality to be the law of the land by judicial fiat, this should be done by legislative action. And conservatives should be leading the way at the state and federal level to pass legislation and, where needed, constitutional amendments guaranteeing marriage equality.
The reason that government should not discriminate between heterosexual and homosexual marriage is because sexual orientation is not a choice; it has been proven beyond all reasonable doubt to be a genetic predisposition. Although we can choose to act in any sexual manner we wish, we cannot choose our sexual orientation. Thus, a gay person can choose to have sex with a person of the opposite sex, but that person cannot “choose” to have an actual heterosexual orientation. This truth is akin to the fact that a left-handed person can choose to use his right hand for certain functions, but he cannot choose to be right-handed. Since sexual orientation is a product of nature and/or God and is not a matter of choice, it should be treated as a protected class under our laws.
Some argue that the term “marriage” applies specifically and exclusively to religious recognition of unions and that marriage equality laws would infringe on the religious freedom of various religious institutions. The problem with this argument is that the term “marriage” is used throughout the federal and various state statutory codes. The government certainly has no business telling any religious institution whether or not to perform or even recognize any particular marriage, and I would oppose any effort to force them to do so. But to the extent that the term “marriage” is used in the various statutory codes, then it should be applied equally to heterosexual and homosexual unions. If we want to reserve the term “marriage” for religion, then we should eliminate it from statutory codes altogether and call all marriages “unions” for legal purposes. (My colleague, Michael Fletcher, argues at Write Side of My Brain  that government should get out of the marriage business altogether. I take no position on this proposal but assert only that as long as the government remains involved with marriage, it should treat heterosexual and homosexual marriages equally.)
The bottom line is that what distinguishes conservatives from liberals is that we are individualists while liberals are collectivists. We believe in individual rights and individual liberties, while liberals believe that the rights of the individual should be subjugated to the needs (or wishes) of the government. It was Republicans who led the fight for women’s suffrage and for civil rights for blacks (notwithstanding a massive amount of historical revisionism in recent decades). Marriage equality is the civil rights issue of our time, and we conservatives should once again lead the way.