"The fundamental right to marry does not include a right to make a State change its definition of marriage. And a State’s decision to maintain the meaning of marriage that has persisted in every culture throughout human history can hardly be called irrational. "

I can change this paragraph only slightly to come up with an absurdity.

"The fundamental right to vote does not include a right to make a State change its definition of suffrage. And a State’s decision to maintain the meaning of suffrage (to be those related by blood to the historically dominant culture taking part in the political process) that has persisted in every culture throughout human history can hardly be called irrational."

States are not free to define away your rights, it's that simple.