The lesson to be learned from the legality of interracial marriage is that just as the law must be blind with respect to the race of persons desiring to marry, so it must also be blind to the sexual orientation of persons desiring to marry. Just as persons desiring to marry cannot be discriminated against on the basis of their race, neither can they be discriminated against on the basis of their sexual orientation. When two persons ask the state for the right to marry, the state must ask no questions about their race or sexual orientation. Just as laws which would discriminate against persons’ marrying on the basis of their race are unconstitutional, so laws which would discriminate against persons’ marrying on the basis of their sexual orientation are unconstitutional.
That’s why the term “gay marriage” (which, I noticed, you were careful to avoid) is misconceived. Laws permitting gay marriage would be clearly unconstitutional, since they would not be blind to the sexual orientation of the persons involved. Such laws would sanction marriage for same-sex couples only if they were homosexuals, thereby taking cognizance of their sexual orientation and discriminating against heterosexuals who wanted to enter into marriage with someone of the same sex. To repeat: just as the law must be blind to the race of persons entering into marriage, so it must be blind to their sexual orientation. Laws sanctioning gay marriage would thus be unconstitutional (not to speak of unenforceable!). [Emphasis added]
So the laws governing marriage must have no reference to the sexual orientation of the persons involved. But that is precisely the situation of the status quo! Under the laws of the status quo no one is denied the right to enter into marriage because of his/her sexual orientation. Two heterosexuals, two homosexuals, or a heterosexual and a homosexual are free to marry, no questions asked, just as persons of different races are free to marry, no questions asked. What they are not free to do under federal law, whatever their race or orientation, is to enter into same sex marriage, simply because there is no such thing. Marriage is by its essence a relation between a man and a woman. But the sexual orientation of the persons involved, like their race, is a matter of complete indifference to the law.
So the legality of interracial marriage actually goes to support the current laws, which are indifferent to both the race and the sexual orientation of the persons involved. Those who want to re-define marriage in such a way that it need no longer be between a man and a woman need to come up with some other argument in support of that redefinition than the appeal to interracial marriage.