John Sides asks why Americans have become less accepting of adultery. One theory:
Even though the divorce rate has decreased since 1980, divorce itself has arguably become more normal and acceptable. It’s hard to get comparable question wordings over a long time span, but these two polls seem suggestive. In a 1954 Gallup poll, respondents were asked “Do you believe in divorce?” 53% said yes and 43% said no. In 2008, 70% of Gallup respondents said that divorce was “morally acceptable”—and that represents an increase even over the 59% figure in 2001. If divorce has become more acceptable, this could lead people to be less favorable to adultery. The logic goes something like this: “If you’re in an unhappy marriage, don’t cheat. Just get divorced.”
Yglesias thinks feminism plays a role.
The Dish 