Am I forgetting the Broccoli Question? If the government can force you to buy health insurance, what can't it force you to buy? The common-sense answer to this, as we've just seen, is straightforward. Nothing. The government can make you pay for whatever it likes--that's where things already stand, and striking down the mandate won't change it. The Constitution as interpreted by the Court these past decades allows the federal government to put your taxes up and use the proceeds to send you a weekly box of broccoli. If Washington instructed you to choose your own basket of fruit and vegetables or else pay a penalty, that would be a smaller infringement of your freedom than the Constitution already allows.
As a practical matter, in other words, there's no "limiting principle". As a legal matter, of course, the Justices who see Obamacare as good policy will bend over backwards to devise one, and those who see it as bad policy will find grounds to be unpersuaded. Justice Kennedy has already told us what this lawyerly criterion could look like.
But I think it is true that if most questions in life are matters of degree, in the insurance and health care world, both markets -- stipulate two markets -- the young person who is uninsured is uniquely proximately very close to affecting the rates of insurance and the costs of providing medical care in a way that is not true in other industries.
"Uniquely proximately very close." Well, something along those lines. But in worrying about whether a relatively liberal method of making you do something is constitutional, having previously determined that a less liberal method of making you do the same thing is perfectly fine, the Court is concerning itself not with an important principle but with a legal technicality. That's not to criticize--it's what courts do. The funniest part is that everybody understands this. If the mandate is struck down, Congress (voters permitting) could turn round and make the penalty a tax, and that would be that. Important principle my eye.
Now of course you can ask whether the Court has been right over the years to use the Commerce Clause to turn the Constitution inside out and dissolve the limits on the economic power of the federal government. That's not an easy question but on the whole I think it has in fact been right. The world has changed, and what we expect of the government has changed. The Constitution had to change as well, and that could be done either by amending it explicitly or having the Court draw on all its reserves of ingenuity and rewrite it judgement by judgement. In America, the Constitution is a quasi-religious document. Its constancy is an inviolable national myth. Changing it therefore falls to the Court and must be done by stealth, with a certain suspension of disbelief on the part of the citizenry. The big disadvantage of amendment by jurisprudence is that it takes an unavoidably political task out of politics and gives it to unelected judges. Obviously, that's also its big advantage.
Whether we like the way the Constitution has been rewritten is beside the point. The thing is, it has been. The Court has all but erased the limits on the economic power of the federal government. So let's not pretend that striking down the mandate would be a victory of principle rather than just a huge embarrassment for the White House, or that upholding it would mark a big new advance of government power. Politically, it matters. Constitutionally, it's a tremendous fuss about not very much.