You need to be more clear, is the interest in procreation? Or is the interest in raising children?
Gay couples do raise children all the time, just like adoptive couple's do. Gay couples do use surrogacy and egg/sperm donation, just like infertile heterosexuals do. Does the state have no interest in protecting these families? I believe it does.
Does the state have no interest in protecting childless marriages? Those past the age of fertility? Then why can they marry, and gay couples with kids cannot?
You are free to believe "creating children" is THE requirement for marriage, but that means denying all couple's who can't have kids and who adopt from marrying. And inconveniencing many gay and straight families, which the state DOES have an interest to protect.
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