In October, the Supreme Court heard arguments involving a 1996 federal law intended to crack down on a new form of child pornography. Which on the face of it sounds simple and uncontroversial. Pornography involving children is repugnant. The children are victims, and the monsters who make and traffic in it are criminals.

But like all attempts to circumscribe free expression, the Child Pornography Prevention Act is not simple at all -- which is why a lower court declared it unconstitutional, and why the Supreme Court is wrestling with it now.

The law has two big free-speech problems -- a strange one that we've never encountered before, and an old familiar one. The strange new problem - the one that inspired Congress to draft and pass the law -- is that personal computers and common software can now be used to create astoundingly lifelike images of human beings.

There are benign examples of this, like the recent PG-13 sci-fi adventure movie Final Fantasy. A cartoon that looks virtually real. But that same state-of-the-art technology can also be used to create astoundingly lifelike pornographic images of children.

Child pornography has been illegal mainly because the children forced to appear in it are victims. But with these computer-generated pictures, the children don't exist -- they are imaginary -- for legal purposes, no different than any drawings, paintings, cartoons or other fictions.

So the difficult new question is this: should we make this kind of smut illegal when no actual human children are involved in its creation? No matter how grotesque it is, how sick and twisted the people who make and watch it are, I don't think we want to criminalize it...to turn these purely imaginary creations into crimes.

That would seem to me like a big dangerous step down the slippery slope of censorship. As everyone from Voltaire to the ACLU has said a million times, "I may despise what you're saying but I'll defend to the death your right to say it."

The other problem with the law is its broadness. Because the intention is to ban computer images that look real, it outlaws the depiction of anything that quote "appears to be a minor engaging in sexually explicit conduct."

Consider the unintended consequences of that: the creators of all sorts of art and legitimate entertainment could be indicted, convicted and sent to prison for up to 30 years. At the Supreme Court hearing the justices dealt with both of these difficult issues...and with our competing, essential needs to protect our children as well as cultural freedom.

Justice Antonin Scalia sarcastically asked a lawyer, "What great works of art would be taken away from us if we couldn't see minors copulating?" The lawyer paused, then mentioned Lolita. In the 1997 film of Nabokov's extraordinary novel, starring Jeremy Irons, the actress who played Lolita was 15 years old.

Justice Scalia responded, again sarcastically: "A great work of art!" Then the lawyer mentioned last year's academy award winning film Traffic starring Michael Douglas. Traffic seems unquestionably against the law. In one disturbing scene, Douglas' down-and-out runaway teenage daughter is shown apparently having sex with her cocaine dealer.

Justice Scalia responded: "With all due respect, this is not the Mona Lisa or the Venus de Milo." But Justice John Paul Stevens was ready with a comeback for his colleague. He asked, "How about Romeo and Juliet?"

The Supreme Court will rule on the case by spring.

This is Kurt Andersen in Studio 360.