Now you see it…

For reasons that are somewhat inexplicable, many in the U.S. are all a twitter about the birth of the newest member of Britain’s royal family. Yes, we have a historic connection to the U.K. They are our closest allies and perhaps the culture most similar to our own.

Even so, they aren’t us, and neither their monarch nor their government is ours.

Earlier this week, British Prime Minister David Cameron inadvertently reasserted one of the fundamental differences between his nation and ours: the limits of free expression.

As reported by CNN, Cameron on Monday rolled out a plan that would, by default, block pornography on most computers, smartphones and tablets. Cameron framed the proposal by saying that “the darkest corners of the Internet” pose a real threat to children.

In response, British wireless and Internet providers have agreed to put adult-content filters on phones, public Wi-Fi networks and home computers in the coming months. By the end of the year, the filters will become the default setting for anyone setting up broadband Internet service at home, Cameron said.

To be sure, we’re not advocating unfettered consumption of pornography. Quite the opposite. Succumbing to morally purulent urges is likely a great cause of many social ills, but rare is the day when the government should have its hand on the spigot of filth.

Perhaps paradoxically, a central function of government is to protect us from ourselves. Left to our own devices, modern miracles such as DDT and asbestos would still be in high use. So would thalidomide and cars without seat belts. Like it or not we need a certain amount of “nannying.”

We need it because we have a demonstrable history of self-immolating at every possible turn.

We also need protection from each other. All of the foregoing examples suffice for this point as well.

This said, Cameron’s proposal isn’t exactly that. Cameron’s proposal in effect says that the government will decide what is unfit for adults to consume; and if they so choose, the adults can decide to opt in to the filth.

The way we do it in America approaches the problem from the other direction. While keeping its mandate to protect us, our system lets us decide what the default position of the filter is. We are free to restrict ourselves, rather than having to defeat the government’s a priori presumptions.

It’s not that we don’t have strong suggestions from the media. Take for example the Motion Picture Association of America’s movie rating system. While it had origins that were wholly puritanical and provincial, it evolved into a system where adults themselves decide their exposure.

Moreover, our government has gotten in a lot of legal hot water when it attempted to decide what was too profane and what was not. Those old enough to remember the public indecency case of the rap group, Two Live Crew, will cede the point.

Furthermore, the U.S. Supreme Court has repeatedly weighed in on similar topics. Perhaps the most famous case in this line is Jacobellis v. Ohio, decided in 1964. In the Court’s decision, Justice William Brennan wrote, “The recognized interest in preventing dissemination of material deemed harmful to children does not justify its total suppression.”

For students of popular culture, this is also the case that produced Justice Potter Stewart’s famous lines, “I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description (“hard-core pornography’); and perhaps I could never succeed in intelligibly doing so. But I know it when I see it…”

Therein lies the complex and painful elegance of our system. We get to decide — without a preemptive filter. What we decide to do in the absence of that filter is a whole other matter.