Legislators in some 20 states are considering making mandatory Merck & Co.'s Gardasil vaccination for the human papillomavirus. In Texas, Republican governor Rick Perry bypassed the legislature and ordered it on his own. The requirement there applies to 11- and 12-year-old girls entering 6th grade.

The benefits seem clear. FDA-approved for females age 9 to 26, the vaccine has been shown to be 100 percent effective at preventing disease from the two HPV strains that account for 70 percent of all cervical cancers. Government estimates are that there will be 11,150 cases and 3,670 deaths from cervical cancer in 2007. So what's not to like?

Plenty.

One argument is that a mandate removes parental authority. Which it does, but so do all mandatory vaccinations. The difference here is that while Perry claims the HPV vaccine is no different from the polio vaccine, polio is transmitted through the breath, while HPV is transmitted by sexual intercourse.

As Robert Zavoski, physician and president of the Connecticut chapter of the American Academy of Pediatrics, explained to the Hartford Courant, "Vaccines previously mandated for universal use are those which protect the public's health against agents easily communicated, responsible for epidemics, or causing significant morbidity or mortality among those passively exposed to the illness." He added, "HPV is not an agent of this sort."

The other argument, which many Christian groups have made in addition to the one about parental authority, is that a mandatory vaccination will encourage promiscuity. This idea has been mocked. District of Columbia councilman David Catania, sponsor of a mandatory HPV vaccine bill, for example, insists, "This vaccine no more encourages sexual activity than a tetanus shot encourages you to step on a rusty nail."

But again, the analogy is faulty. There is no biological urge to step on rusty nails. There is, however, a powerful urge to have sexual intercourse that begins at puberty. It's an urge that nations and religions throughout history have sought to control in various ways because sexual intercourse, while pleasurable to the participants at the time, can have consequences that are deleterious to the individuals later as well as to society as a whole.

When you insist that 11-year-old girls receive shots to protect them from dangers attending sexual intercourse, you are sending them a message. In fact, you're even sending their male peers a message. And it is one that conflicts with the message that sexual activity is best left to people who are more mature.

Still, what about those preventable infections and cancers? HPV infection is usually fairly benign; in fact, a study just released by the CDC says about 27 percent of U.S. females aged 14 to 59 years have it. Importantly, only 2.2 percent of those women are carrying one of the two virus strains most likely to lead to cervical cancer. Usually infection is asymptomatic; but in a minority of cases it leads to tiny cauliflower-like bumps on the genitalia (or anus) that will disappear on their own or be zapped off by a doctor. And in a much smaller minority of cases, infection leads to cell irregularities that become cervical cancer.