In a post at the conservative blog RedState, one Hogan neatly sums up the conservative position. On constitutionality, he argues that the highest law "should [not] be used by the Judiciary to invalidate the will of the people based on a protection that does not exist in the Constitution."
As for objective law, Hogan believes that it's "rational" to outlaw same sex marriage.
[I]t seems to me that we human beings may well have more than a "rational basis" to recognize marriage as it has been recognized around the world for literally thousands of years---the union of a man and a woman. For reasons of pro-creation and parenthood, to start with, but also for reasons of faith and morality, for some of us, any marriage other than such a union can never be, whatever society says, a "marriage" at all.
Notice first the fallacy of appealing to "thousands of years" of tradition before, correctly, dismissing the "will of society" as a legitimization of any measure. Presumably, the will of the people matters to Hogan only when a majority happens to agree with him.
Majority rule absent objective law equals mob rule however and it's anything but rational, let alone legitimate.
No matter Hogan's appeals to "faith" and "morality" (what morality?), there is no rational reason for denying homosexual couples to marry.
(As for procreation and parenthood---I have yet to see any study underwriting the blatant assumption that gays make for lesser parents. Besides, if it were so that children are best raised by a man and a woman, what to think of all the divorces and single parents out there? Should they be denied the right to have children? And just what has this to do with marriage anyway? What about all the unmarried couples who have children and what about all the gay couples who have no children? Some may like to cry "what about the children?" whenever they see something they don't like but that doesn't make it rational at all.)
Is there a constitutional basis for outlawing gay marriage perhaps? The Constitution, of course, doesn't say anything about marriage explicitly but it does provide that citizens of the United States are equal before the law. As long as government has a place in regulating marriage, which is to say that they are recognized as such by the law, it would seem fairly obvious that no arbitrary restrictions based, for instance, on race, heritage or sexual preference, ought be imposed on it.
Chief US District Judge Vaughn Walker, who repealed California's marriage law last Wednesday, recognized this when he ruled that the state's infamous Proposition 8 failed "to advance any rational basis in singling out gay men and lesbians for denial of a marriage license." What's more, according to Judge Walker, "Moral disapproval alone is an improper basis on which to deny rights." And that's about all there's to be said on the legitimacy of same sex marriage.