I think the ACA, including the individual mandate, is clearly Constitutional, but I'm agnostic about whether the militia act really tells us anything about what the framers would say about the individual mandate. I've seen reasonable arguments both ways.
I'm quite positive, however, that Jack Balkin's argument about civic republicanism and the individual mandate is mistaken. He's correct, as far as I know, here:
The requirement to join the militia (and purchase arms for the defense of the state) was an aspect of civic republicanism-- the political idea that citizens had a duty to work toward the public good and make sacrifices on behalf of their fellow citizens and the republic (the res publica, or public thing).
What is lost in the debate over the individual mandate is that the point of the individual mandate is also civic republican in nature. It requires citizens to make a far less significant but also public-spirited sacrifice on behalf of other Americans who cannot afford health insurance.The individual mandate is not about personal sacrifice. Nor is it about virtue, or public action -- all of which are ideas associated with civil republican thought. The individual mandate is simply a solution to a collective action problem: proponents believe that we're all better off with a well-functioning health care insurance system, but that without the mandate many of us will have a short-term interest in gaming the system and opting out, thereby destroying the very system we want to preserve. It's not about public action at all. It's about private benefits.
That's important, I think, for ACA supporters -- and for liberals in general -- to understand, and perhaps to emphasize. It's true that there are times that liberals support measures that could fit well into a civic republican frame -- Democratic initiatives on voting rights, or Teach for America. But most of the liberal agenda, whether it's Social Security, climate change, or civil rights, fits comfortably inside the general rubric of self-interest. That is, as Matt Yglesias has pointed out, the idea that contemporary American conservatives are the true heirs of Lockean liberalism while contemporary American liberals are cut off from "classical" liberalism is hogwash.
Basically, I see no reason at all for (contemporary) liberals to abandon selfishness to conservatives when it comes to social insurance programs, including health care. There's nothing noble about the motives involved in making an important market work better (or, as with Social Security or Medicare, supplementing markets with public programs when market solutions aren't likely to work). Farsighted, perhaps, but noble? Not really.