David Cole explains concisely why it doesn't make sense to rule the ACA unconstitutional based on existing precedent:
On this theory, the Supreme Court has upheld federal laws that restricted farmers' ability to grow wheat for their own consumption and that made it a crime to grow marijuana for personal medicinal use, even though in both instances the people concerned sought to stay out of the market altogether.5 The Court reasoned that even such personal consumption affects interstate commerce in the aggregate by altering supply and demand, and that therefore leaving it unregulated would undercut Congress's broader regulatory scheme.
Under these precedents, a citizen's decision to forgo insurance, like the farmer's decision to forgo the wheat market and grow wheat at home, easily falls within Congress's Commerce Clause power. When aggregated, those decisions will shift billions of dollars of costs each year from the uninsured to taxpayers and the insured. As a practical matter, there is no opting out of the health care market, since everyone eventually needs medical treatment, and very few can afford to pay their way when the time comes. (Those who refuse all medical treatment for religious scruples are an exception, but they are exempt from the mandate.) That one might affix the label “inactivity” to a decision to shift one's own costs to others does not negate the fact that such economic decisions have substantial effects on the insurance market, and that their regulation is “an essential part of a larger regulation of economic activity.”
Cole also reiterates the most common liberal critique of the "states' rights" arguments within the American historical context:
In this respect, Judge Hudson and the Virginia attorney-general are situated squarely within a tradition—but it’s an ugly tradition. Proponents of slavery and segregation, and opponents of progressive labor and consumer laws, similarly invoked states’ rights not because they cared about the rights of states, but as an instrumental legal cover for what they really sought to defend—the rights to own slaves, to subordinate African-Americans, and to exploit workers and consumers.
I don't think it's true at all that having libertarian beliefs means you're a racist or you support child labor. In the American historical context, though, there's no question that libertarian arguments have been hijacked and given political significance through people eager to deploy them in service to a particular ethnic, economic, or cultural hegemony. As Damon Root has written, there were some libertarians who deployed ideological arguments against Jim Crow. But the Southern states that went for Barry Goldwater in 1964 weren't doing so because they wanted to implement their own local desegregation efforts. They did so because Goldwater's libertarian positions on civil rights offered a (barely) superficially non-racist moral and constitutional defense of segregation and racial discrimination.
Similarly, you get the sense that Republican opposition to the ACA has to do at least in part with the idea that Republicans don't think covering the uninsured is a moral imperative because if you can't afford health insurance, it's because you're some sort of immoral human parasite. That doesn't bear on whether or not the ACA is constitutional, but I think it does help explain why this particular libertarian argument has gained so much traction. It's not like Republicans are listening very carefully about what libertarians have to say about heavy-handed government intervention and same-sex marriage.
