Congress has been trying to stop kids from seeing online pornography since 1996. Its first attempt, the Communications Decency Act, was overturned by the Supreme Court, and its second attempt, the Child Online Protection Act (COPA), seems destined for the same fate. The court already has upheld a preliminary injunction blocking enforcement of COPA, and a federal judge recently made the injunction permanent.

For more than a decade, then, parents have stood by helplessly as their children have been bombarded by dirty pictures. Well, not exactly. As U.S. District Judge Lowell Reed noted when he issued his injunction, filtering software used by parents and Internet service providers is much more effective than COPA would have been at keeping porn away from kids (or perhaps I should say "keeping kids away from porn," which better describes the reality of the situation).

The insistence that there nevertheless ought to be a law, which could still be heard in the wake of Reed's decision, betrays a disregard for the damage done to freedom of speech by heavy-handed efforts to make the Internet safe for children. It also reflects a knee-jerk statism that demands a top-down, one-size-fits-all solution even when diverse, decentralized responses clearly work better.

Reed concluded that COPA is both too narrow and too broad. It is too narrow because it does not apply to Web sites based in foreign countries, which account for something like half of online pornography. It is too broad because it covers not just pornography but any discussion or depiction of sexuality deemed "harmful to minors"--i.e., anyone under 17.

The law thus could apply to material, such as sex education, that is inappropriate for 3-year-olds, even if it's OK for 16-year-olds, never mind adults. COPA prohibits "commercial" sites (those that sell content or ad space) from making such material available to minors, threatening violators with a six-month prison sentence and fines of up to $50,000 a day.

Web site operators can escape those penalties "by requiring use of a credit card, debit account, adult access code or adult personal identification number" before allowing access to potentially objectionable text or pictures. Any such requirement would impose costs on Web sites, compromise readers' privacy and deter adult visitors. How likely would you be to cough up a credit card number for the privilege of reading an article?

Given this reality, Web sites would have a strong incentive to steer clear of anything sex-related that might be considered inappropriate for children. Without a single prosecution, the law could have a substantial effect on material available to adults.

Worse, as Reed concluded based on expert testimony, none of the "age verification" options mentioned in COPA is a reliable way to verify age. The law thus would cost Web sites money, inconvenience adults, reduce readership and chill online speech without accomplishing the avowed objective of shielding minors from pornography.

Filtering software, by contrast, is easy and cheap (often free) to use, and it can be close to 100 percent effective at blocking porn, whether it originates in the United States or abroad. Even the worst-performing programs, Reed found, block around 90 percent of sexually explicit material.

While mistakenly preventing access to unobjectionable Web sites remains a problem, dynamic filtering using improved algorithms has reduced the frequency of over-blocking to as low as 5 percent, and parents can always add erroneously blocked sites to the "white list" of approved addresses. Filters can be adjusted based on the age and maturity of the child (even for several different children) and the subjects parents consider inappropriate (e.g., sex, violence, drugs, racism). Passwords prevent kids from circumventing the controls.

This kind of flexibility is impossible to achieve through legislative diktat. Filters allow parents to choose the kind of protection that best suits their values and their children. Most important, unlike laws that threaten to impose preschool propriety on everyone, they can be turned off by grownups.