It has become known as the Broccoli Hypothetical. In oral arguments over whether ObamaCare violates the Constitution by forcing people to buy insurance, federal Judge Roger Vinson asked, "If they decided everybody needs to eat broccoli because broccoli makes us healthy, they could mandate that everybody has to eat broccoli each week?"

This is the reductio ad absurdum: a means of disproving X by showing that if X is carried to its logical conclusion, then the result is absurd. If Congress can make you buy insurance—not as a condition of exercising a privilege, such as driving, but as a condition of merely being alive—then it can make you buy anything, including broccoli and GM cars. But it would be absurd for Congress to make you buy broccoli or a car. Therefore, it can't make you buy health insurance, either.

There are two problems with this. First, some ObamaCare supporters say that, in fact, Congress could indeed force you to buy broccoli or GM cars. One of them is Erwin Chemerinsky, dean of the University of California, Irvine, School of Law. "In theory," he says, "Congress could use its commerce power to require people to buy cars. . . . Power can be used in silly ways, and the Constitution isn't our protector against undesirable government actions—only unconstitutional ones."

(Article continues below video "Wheat, Weed, and ObamaCare: How the Commerce Clause Made Congress All-Powerful.")

Supreme Court Justice Elena Kagan took the same position during her confirmation hearings, when Sen. Tom Coburn asked whether Congress had the power to make people eat three fruits and three vegetables each day. "Sounds like a dumb law," Kagan answered, "but I think that the question about whether it is a dumb law is different from . . . the question of whether it's constitutional." Or as one commenter on the Volokh Conspiracy blog put it even more succinctly, "Stupid legislation does not become unconstitutional by reason of being stupid."

True enough. What's more, forcing people to buy a product might not seem any kind of a stretch for a government that already has the power to conscript people into wartime military service. Indeed, the Supreme Court upheld a variety of WWII-era economic measures on precisely those grounds. So a fair number of people would contend that the reductio part of the reductio ad absurdum does not apply, since no great leap in federal power is being made.

It's also becoming apparent that a fair number of people would challenge the absurdum part, too. Forcing people to buy broccoli is not absurd at all, they would say; in fact, it is good public policy.

For evidence, consider a few recent developments:

• Arizona may slap a fee on Medicaid recipients who smoke or are obese.

• New York Mayor Michael Bloomberg wants to forbid buying soft drinks with food stamps.

• The Los Angeles Times recently published a lengthy editorial supporting a "fat tax" on the grounds that obesity raises health-care costs. Americans "should be free to eat what they want," the newspaper contends, "as long as they bear the cost of their personal choices."

• The federal government has proposed new rules that would prohibit advertising directed at children of foods deemed unhealthy.

• Little Village Academy, a public school in Chicago, has banned homemade lunches, explicitly to foster healthy eating and combat child obesity.

• Los Angeles is banning fast-food restaurants in South LA, where poverty and obesity are widespread.

• First Lady Michelle Obama has made reducing child obesity her cause.

• The Georgia "Stop Child Obesity" billboard campaign has ignited controversy with its stark anti-fat message.

These developments seem to follow the arc of the anti-smoking crusade—focusing first on children, public funding and advertising, but spreading to other realms like ripples in a pond. Taken individually, a few of them make sense. For example, there is nothing wrong with setting conditions on how recipients spend money from federal nutritional programs. And since nobody is in favor of children getting fat, there's little reason to object to the general goal of the first lady's "Let's Move!" campaign.

Taken collectively, however, these eat-your-vegetables developments point to a profound shift in how Americans think about government's role in society. For the most part, government intervention in private activity has been considered justifiable only to prevent the violation of rights. If Joe has broken into Fred's house and is stealing Fred's stuff, then the government should stop him. But the government cannot make Joe exercise just because Fred thinks he should.

More and more, it is claimed that Joe does not have to violate Fred's rights before the government can get involved. It is enough for Joe merely to do something that affects Fred in some way. But since just about everything anybody does can be said to affect somebody in some way, this amounts to a license for a government of infinite scope. More and more people seem to think because "a healthy population is good for everyone," as The New York Times recently put it, government should make people stay healthy as well. And as the federal government underwrites more and more of the health care system, it gains more and more prima facie justification for ordering people about.

Those who bring up the Broccoli Hypothetical, as Vinson did, seem to think they have played a trump card. Unfortunately, they might just be giving advocates of the nanny state ideas.

A. Barton Hinkle is a columnist at the Richmond Times-Dispatch. This article originally appeared at the Richmond Times-Dispatch.