McArdle believes that marriage equality will make Americans more morally traditional:

When traditional marriage, with its expectations of monogamy and longevity, no longer means excluding gays, expect it to get more popular among affluent urbanites.

To be sure, it’s already popular–affluent urbanites are now quite conservative in their personal marital habits. They’ve just been reluctant to shame those who don’t follow suit. But with marriage freed from the culture-war baggage, we now have an opening for change. Think it can’t happen? Consider the cigarette. It was shocking for a woman to smoke on in public in 1880, nearly mandatory in 1940, and increasingly shocking in 2013 (for either gender). I wouldn’t be surprised to see out-of-wedlock childbearing follow a similar course.