Hester Prynne, data suggests, wouldn't get much of a break today.

More Americans tolerate things we formerly considered taboo, such as premarital sex, divorce and gay relationships. But there's one glaring exception: We condemn adultery like it's 1642.

According to a recent Gallup poll, 91 percent of adults consider extramarital sex wrong. That's a notable change from 40 years ago, when the National Opinion Research Center found that less than 70 percent of respondents considered adultery "always wrong."

While those results may seem contradictory, they're not, experts say.

People today enjoy more freedom to pursue love, such as exploring premarital sex and having more control over when to enter or exit a marriage. But with more freedom comes more accountability, and lying is the one vice that most of us agree is wrong.

"There's a lot more emphasis now on authentic, honest relationships," said William Doherty, a professor of family social science at the University of Minnesota. "Extramarital affairs that are secret go against the modern trend. Dishonesty is the one thing both liberal and conservative people can condemn."

One possible reason for the shift in attitudes is that people are getting married later. According to the U.S. Census, men marry at age 29 on average, and women marry at 27. In 1950, men married at 23 or 24, women at 20 or 21.

We still value marriage, but its meaning has changed.

Previously, Americans got hitched to join what marriage historian and Evergreen State College Prof. Stephanie Coontz calls "respectable society." Now, more people consider marriage a capstone — something you do after finding a certain amount of financial, professional and emotional success, as well as romantic experience. Getting married is less about respectability, Coontz says, than individual happiness.

"We respect marriage as a relationship more than any other time in history," Coontz said. "Because of that, we expect more intimacy, more fairness and more fidelity."

Of course, we have traditionally practiced a double standard: Extramarital sex wasn't an absolute no-no for men, but it was for women. And, in cases of divorce, the wives still suffered from the public humiliation, even when it was the men who had cheated.

Mary McNutt of Minneapolis said her husband revealed in 1979 that he was having an affair and filing for divorce. Even though she tried to save the marriage, her neighbors wouldn't let their kids play with her kids when they found out.

"Now divorce is so common," said McNutt, "but I was scared to death."

Coontz says that it wasn't until the mid-20th century, particularly after the rise of feminism, that women began to fight that double standard — in part by gaining financial independence. (In 1960, married women were the sole breadwinners in just 3.5 percent of families.) Married women now make up 47 percent of national household earnings, according to a report by the University of New Hampshire.

"As women have gained the right to work and earn more income," said Coontz, "they can now, in a sense, put their money where their mouth is and say, 'If you don't behave, I will leave you.' "

After her divorce, McNutt got two graduate degrees and became a psychologist. If her husband cheated on her today, she says her reaction would be different.

"I would not tolerate that and try to put it together now," she said. "I'd say, 'You're out the door. Goodbye!' "

Given the strong stand against adultery, you'd think people would be cheating less than in the past. Some statistics actually support the contrary: According to a University of Washington study, the rate of people over the age of 60 who admitted to sexual infidelity sometime during their lives increased between 1991 and 2006 from 20 to 28 percent in men and from 5 percent to 15 percent in women.

But more people admitting to extramarital affairs shouldn't overshadow how gender equality has caused "very powerful changes" in views of sexuality, says Ira Reiss, a pioneer in sexual science research and former professor at the University of Minnesota. Behaviors are more spontaneous than attitudes, he says.

"There is still a significant correlation between attitude and behavior even though a lot of people who would say it's wrong get caught up in the heat of the moment," he said. "An awful lot of those people are there once or twice, and then it's over."

Andrew Wagaman • 612-673-4645