Slate's wonderful "Everyday Economics" columnist Steven E. Landsburg writes that internet porn reduces incidents of rape, and that violent movies reduce violent crimes:
What happens when more people view more [porn]? The rise of the Internet offers a gigantic natural experiment. Better yet, because Internet usage caught on at different times in different states, it offers 50 natural experiments.
The bottom line on these experiments is, "More Net access, less rape." A 10 percent increase in Net access yields about a 7.3 percent decrease in reported rapes.
OK, so we can at least tentatively conclude that Net access reduces rape. But that's a far cry from proving that porn access reduces rape. Maybe rape is down because the rapists are all indoors reading Slate or vandalizing Wikipedia. But [Clemson] professor [Todd] Kendall points out that there is no similar effect of Internet access on homicide. It's hard to see how Wikipedia can deter rape without deterring other violent crimes at the same time.
psychologists have found that male subjects, immediately after watching pornography, are more likely to express misogynistic attitudes. But as professor Kendall points out, we need to be clear on what those experiments are testing: They are testing the effects of watching pornography in a controlled laboratory setting under the eyes of a researcher. The experience of viewing porn on the Internet, in the privacy of one's own room, typically culminates in a slightly messier but far more satisfying experience—an experience that could plausibly tamp down some of the same aggressions that the pornus interruptus of the laboratory tends to stir up.