Let's travel for the moment back to 1942:
"We need to regulate crop production in this time of crisis, or agricultural markets will collapse. But we have farms growing feed grain in addition to their allotted crops to feed their livestock. Let's pass a law that says if you can't feed your livestock out of the crops you're permitted to grow, you must buy your feed grain from another source."(See Wickard v Filburn). The outcome is the same, with the arguable distinction that the farmer is left with the "freedom" to either sell all of his livestock or to let his animals starve, neither of which were likely.
"Horror of horrors, no! That would compel the farmer to engage in commercial activity! The next thing you know we would be forcing people to buy broccoli!"
"Let's say you're right - how do we get him to buy his feed grain from somebody else if we don't impose that requirement?"
"Simple. We simply tell him he can't grow the additional grain"
Now let's move back to the present:
"We want to allow universal access to health insurance, but we can't do that if we allow free riders - if people can avoid buying insurance until they're sick, insurance companies will take a loss on every customer. We need to impose a mandate. Let's require everybody to have insurance, and impose a small penalty on those who don't obey that mandate."The law professors who created and pushed the "activity vs. inactivity" distinction are patting themselves on the back for the court's effective 5:4 vote recognizing that distinction. But as constitutional doctrine goes, it's a one-off. To the extent that Congress is using its actual powers in a valid manner, the distinction calls into question only the language the use when drafting legislation.
"Horror of horrors, no! That would compel the individual to engage in commercial activity! The next thing you know we would be forcing people to buy broccoli!"
"Let's say you're right - how do we get people to buy health insurance if we don't impose that requirement?"
"Simple. We do exactly the same thing, but call it a tax!"
"You must buy or pay a penalty...", no, that compels activity. Make it "You can't make or grow..." or "You must buy or pay a tax."It's funny in a way that, in order to appease the factions that have created and pushed the "activity vs. inactivity" distinction. However he followed that homage by holding that the mandate was effectively a tax, and thus a noncontroversial exercise of the powers of Congress. His analysis was thus much less about whether Congress was properly exercising its powers, than it was of whether Congress used the right language when engaging in what he accepted to be a proper exercise of its power.
Roberts chose to take an expansive view of the power to tax, endorsing the idea that Congress can use a tax as a tool of coercion. That would be more significant if there were a significant chance that Roberts would take the same position in a future context and convince a majority of the court to follow his lead. I don't expect that to happen, as I believe Roberts was making an argument of convenience.
Here's the thing: If the possibility of a "broccoli" mandate is a genuine danger, if it necessitates creating a wholly new constitutional doctrine, supported neither by the text of the Constitution nor by any Supreme Court precedent, if it requires holding a valid exercise of Congressional power to be unconstitutional because some future Congress might attempt to impose an improper mandate, why wouldn't that very same slippery slope apply to a coercive tax?
If you focus throughout on the substance of the law - is this a proper exercise of Congressional power - there's no need to play that sort of game. Given the structure of the reform law, a mandate was necessary to avoid free riders. But for the newly minted "activity vs. inactivity" doctrine, this would have been a rather simple case, turning on whether Congress was exceeding the scope of its powers. Instead, as a palpably angry minority of the court wanted to overturn the entire ACA based upon the "broccoli mandate" argument, Roberts felt compelled to join the game.
In the longer term, the "activity vs. inactivity" distinction is a footnote to history. Congress will watch its wording. In one future, this entire case becomes a footnote to history. Future justices move away from the type of right-wing activism favored by those who concocted the activity-inactivity distinction, and we return to the type of Commerce Clause analysis we've seen for the past seventy years. In another world, future justices build upon other parts of the decision, refining "activity vs. inactivity" into a test that can be used on presently non-controversial issues, following Roberts' proposed lead by creating new limits on Congress's spending power, and moving us away from the legal doctrines of the New Deal era. In that future, Roberts can claim to have laid the cornerstone of the new jurisprudence. Either way, his opinion does a very good job of protecting his own reputation and eventual legacy.
Update: Richard Epstein summarizes how dramatically Roberts' position on taxation departs from precedent.