Despite what those on the far right would have us think, marriage as an institution has changed much over the years. Historian Stephanie Coontz, in a recent article on the topic, notes:

Until the 1980s, courts said that the husband must support the family; the wife had no such duty. Wives were charged with keeping house, rearing children and providing other personal services. That is why a man could not be charged with marital rape and a woman could not sue for loss of personal services in the event of her husband's death. Only in the 1980s did courts redefine marriage as a union of two people with reciprocal, not complementary, duties.

Once marriage came to be seen as an institution bringing together two individuals based on mutual affection and equality, without regard to rigidly defined gender roles or the ability to procreate, it's not surprising that gays and lesbians said, "That now describes our relationships too, so why can't we marry?" If you don't like these changes in the institution, blame your grandparents, not the gay and lesbian couples seeking entry into this new model of marriage.

The push for women's rights within marriage was thus the instigator of change that opened the doors for same-sex couples to consider the institution. Now, it is the push for LGBT equality that is helping to remove the last vestiges of inequality even in opposite-sex relationships. Proof that equality has a way of spreading in directions we do not always foresee or intend, but which benefit us all.