With or without separation of church and state, the state’s interest in marriage has never been about individual rights and privileges. It was about the most sacred of responsibilities. And governments of all kinds wisely chose to protect the family as the creator and incubator of future generations by promoting the fully committed union of a man and a woman. Gender and gender differences matter, especially to children. Mothers and fathers are not interchangeable, which is why changing the definition of marriage is like trying to change the chemical composition of water. It may seem more egalitarian, diverse or tolerant, but it won’t be life-sustaining H2O.