The New York Times carries an op-ed on the heterosexual revolution, in which marriage went from a mandatory economic and political institution to a voluntary love relationship.
Stephanie Coontz writes (excerpt):
Giving married women an independent legal existence did not destroy heterosexual marriage. And allowing husbands and wives to construct their marriages around reciprocal duties and negotiated roles – where a wife can choose to be the main breadwinner and a husband can stay home with the children- was an immense boon to many couples. But these changes in the definition and practice of marriage opened the door for gay and lesbian couples to argue that they were now equally qualified to participate in it.