But some porn-haters declare that X-rated material does more than just disgust them. They contend that it contributes to significant social harm. In The Porn Trap (2008), psychotherapists Wendy and Larry Maltz assert that it's a significant factor in sexual irresponsibility and .

The late feminist activist, Andrea Dworkin, argued that by depicting women as men's willing sexual playthings, porn contributes to rape. Her disciple, Robert Jensen, writes: "pornography alone doesn't make men rape...[but] it may activate coercive tendencies." And porn critic Diana Russell argues that porn undermines men's inhibitions against rape and spurs some to commit it.

Strong accusations. But are they true? The advent of Internet porn provides surprising answers.

The Internet became a major force in everyday life in the late 1990s. Before then, porn was available in adult stores, through X-rated video rentals, and on some newsstands. But with the arrival of the Internet, porn availability exploded. It was just a click away 24-7 for free in tens of millions of homes and offices. In 1997, 16 percent of American adults used the Internet regularly. By 2005, the figure had quadrupled to 65 percent. The Internet has also made porn much more available to impressionable kids. How many kids, ages 10 to 17, have viewed Internet porn? According to a recent report in the journal Pediatrics, 42 percent.

If porn is a significant contributor to social harm, we would expect to see substantial increases in sexual irresponsibility, divorce, and rape since the late 1990s when the Internet suddenly made X-rated material much more available to those who might instigate sexual mayhem, overwhelmingly men.

Guess what. Since the arrival of Internet porn:

* Sexual irresponsibility has declined. Standard measures include rates of abortion and sexually transmitted infections. According to the Centers for Disease Control and Prevention (CDC), since 1990, the nation's abortion rate has fallen 41 percent. The syphilis rate has plummeted 74 percent. And the gonorrhea rate has plunged 57 percent.

* has declined. The CDC says that since 1991, the proportion of teens who have had intercourse has decreased 7 percent. Teen condom use has increased 16 percent. And the teen birth rate has fallen 33 percent.

* Divorce has declined. Since 1990, the divorce rate has decreased 23 percent.

* Rape has declined. According to the Justice Department's National Victimization Survey, since 1995, the rate has fallen 44 percent.

Why would social ills decline as porn becomes more widely available? No one knows. But the one thing porn really causes is . Internet porn keeps men at home one-handing it. As a result, they're not out in the world acting irresponsibly-or criminally.

I'm not arguing that porn is utterly harmless. Some men consume it so compulsively that it interferes with their lives. They need . Some women become distraught when they discover that the men in their lives enjoy porn. They might benefit from couple therapy. And to the extent that porn is a sex educator, it teaches lovemaking all wrong. More about this in a future post.

But the evidence clearly shows that from a social welfare perspective, porn causes no measurable harm. In fact, as porn viewing has soared, rates of syphilis, gonorrhea, teen sex, teen births, divorce, and rape have all substantially declined. If Internet porn affects society, oddly enough, it looks beneficial. Perhaps mental health professionals should encourage men to view it.