The prostitution scandal that toppled Eliot Spitzer has turned a spotlight of attention on prostitution and sexual hypocrisy. Citizens and the press were shocked — shocked — that the governor was paying for sex.

But is prostitution all that rare? In fact, it is relatively common. In 2006, the National Opinion Research Center, surveying 2,400 American adults nationwide, asked whether they had ever either paid — or been paid — for sex. One in six men admitted they had done so at some point in their adult lives, as did one in 46 women.

As commonplace as the behavior is, many people have found it astonishing that a man of Mr. Spitzer’s intelligence and educational accomplishment could be dominated by something as low-brow as prostitution.

In truth, brains are not the issue: 19% of men with education beyond college have patronized the sex trade, versus 16% of people who didn’t go to college at all. In spite of slightly higher education levels, men who have paid for sex earn about 9% less in income per year than non-payers.

There are a few other demographic surprises as well. First, the use of prostitutes is not a function of youth. Men who have paid for sex are seven years older, on average, than those who have not paid for it.

Nor is the lack of religion in one’s life a major predictor of paying for sex. Indeed, men who attend a house of worship every week are barely less likely to have paid for sex than men who attend less than once a year or never — the difference is just one percentage point.

A more substantial difference involves political ideology: Self-described “liberal” or “very liberal” men are about a third likelier than “conservative” or “very conservative” men to have paid for sex at some point in their lives.

Even more ordinary than the use of prostitutes is extramarital sex, which one in four married men admit they’ve had, as do one in six married women. In a bizarre twist, the man who replaced Mr. Spitzer as governor, the former lieutenant governor, David Paterson, started his tenure last week with an admission that he had had relationships with other women than his wife. His allegation to the press that he has a “marriage like many Americans, maybe even like many of you,” may be a pathetic excuse, but it is manifestly true in the data.

What spectacularly differentiates Mr. Spitzer’s case from Mr. Paterson’s is not the licentiousness of the actions, but Mr. Spitzer’s hypocrisy in portraying himself as a straight arrow while legally denouncing the very activities in which he himself was engaged. But even sexual hypocrisy is fairly unremarkable.

In 1996, NORC presented 1,200 people with the following statement: “There is nothing wrong with prostitution, so long as the health risks can be minimized. If consenting adults agree to exchange money for sex, that is their business.” Fifty-three percent of adults “disagreed” or “disagreed strongly” with this statement.

What about those who had paid for sex? Fifty percent disagreed. In other words, just because people buy sex doesn’t mean they are likelier than others to think it’s alright to do so. Similarly, in 1998, 58% who had cheated on their spouses said that such infidelity was “always wrong.”

So sexual hypocrisy is fairly widespread. That might not be a bad thing; after all, it is said that the man who isn’t a hypocrite has either no sin or no morals. You might argue that if the former is impossible, hypocrisy is preferable to the latter.

Where Mr. Spitzer is unusual is not in his immorality or even his hypocrisy, but in his lack of humanity toward others in treating private sin as a legal matter for his own career gain.

Mr. Brooks, a professor at Syracuse University’s Maxwell School and a visiting scholar at the American Enterprise Institute, is the author of the forthcoming book “Gross National Happiness.”