It wasn't until the Supreme Court case Griswold v. Connecticut in 1965 that married couples won the right to contraception. Assisted reproduction, such as it was back then, was also frowned upon. [7 Surprising Facts about The Pill] http://www.livescience.com/14691-surprising-birth-control-pill-facts.html "In the 1950s, at least two state courts held that assisted reproduction was adultery and the child was illegitimate," Coontz said.
Laws such as this gradually got overturned, Coontz said, making marriages far less gendered. At the same time, expectations that a married couple must procreate have declined and assisted reproductive technology is far more acceptable for couples who can't have kids the old-fashioned way.
In other words, same-sex couples haven't changed marriage for straight people, as opponents of same-sex marriage often argue, Coontz said. Heterosexuals changed marriage first.
"It's the opposite sequence than what is described by opponents of same-sex marriage," she said.
Opponents of same-sex marriage tend to hold more traditional, gendered views of marriage than supporters, Coontz said. But given that heterosexuals aren't quizzed on their plans for splitting up the household chores or having babies before being handed a marriage license, it's hard to construct legal arguments around that view.