As Scott Lemieux says, one of the odder arguments against the constitutionality of the Affordable Care Act is the argument that if the federal government has the authority to fine people for not buying health insurance as part of a comprehensive insurance regulation scheme, then there are no limits on federal power.
If anything, I think this is silly on a deeper level than Lemieux suggests. For example, suppose congress passed a law saying “selling books across state lines that criticize US policy in Afghanistan” is illegal. Well, they couldn’t do that notwithstanding the clearly interstate and commercial nature of the activity in question. That’s because there are sharp limits on congress’ authority to restrict freedom of expression and that authority is maximally limited when the expression at issue is political in nature. Similarly, an “individual mandate” for jurors to pay a fine if they rule against the prosecution in a criminal proceeding would be unconstitutional. It’s not difficult to think of limits to congress’ authority to regulate the national economy.
The real issue here is the longstanding dispute over whether or not congress has the authority to regulate the national economy. For the past 75 years or so that’s been the practice, and it was the practice in the Early Republic. It’s certainly true that at times in the 19th century the Supreme Court took a different view of the question, and then since the New Deal a dissident minority has criticized this practice. And it’s certainly true that the authority to regulate the national economy is a lot of authority. But it’s clearly not unlimited authority. Many ACA critics seem to want to hold the view that the law is unconstitutional without committing themselves to wholesale rollback of congressional authority to regulate the national economy. But it would be exceedingly strange to argue that Congress does have authority to regulate the national economy but is limited in the methods by which it can do this and that those limitations aren’t the ones written down in prior caselaw but instead are just ones ginned up ad hoc to rule a single law out of bounds.