A family headed by one woman and one man is usually agreed to be the best unit for raising well-adjusted children, one of the primary interests of the People. Therefore, it is appropriate for the State to encourage marriage. Childbearing and rearing aren't the only reasons that individuals marry, but heterosexual marriage is a package deal. The State interest is in propagating the People, and the People demand that all individuals have the right to heterosexual marriage.
Homosexual marriage is another matter. It does not generally produce children or rear them in a beneficial environment. Therefore, the State has no interest in promoting or officially recognizing homosexual relationships. The People, whenever the State deigns to ask, reject homosexual marriage -- they don't want what they consider an ancient tradition, a constitutional element of their civilization, altered by a minority that cannot explain to their satisfaction why this alteration should be made.
(I'm not arguing that gays shouldn't raise children, or that they should; only that the best method is the nuclear family, providing the integral diversity of a mother and a father. It's the responsibility of the State to encourage that best method through official recognition of the tradition of marriage.)
I think it is valid to argue that gays have no right to claim other people's children because they can't produce their own.
"The State interest is in propagating the People, and the People demand that all individuals have the right to heterosexual marriage. Homosexual marriage is another matter."
I get it!!! The only way for a homosexual couple to have children is to get one from a heterosexual couple. It negates the whole concept that they are the same or can ever BE the same as a heterosexual couple!!!