The Sixth Circuit upheld the individual mandate:
But the majority agreed with Neal K. Katyal, the acting United States solicitor general, who argued that individual choices to not purchase insurance, when taken in aggregate, have clear commercial effects because they shift the cost of caring for the uninsured to other payers.
The judges adopted Mr. Katyal’s argument that because the need for health care is unpredictable, it is impossible for individuals to opt out of the market. And they agreed that cost-shifting was inevitable so long as the federal government required hospitals to treat those who show up with life-threatening conditions.
An earnest libertarian would question the "must-treat" mandate, which started us on this slippery slope. IIRC, I did question it somewhere, but Google fails me.