You don't have to be lawyer to have common sense.
We know, or I think we know, that a single-payer system -- in which the government collects taxes, and uses the revenue to provide health insurance -- would be constitutional. I mean, I don't think the court is about to strike down Medicare.
Well, ObamaRomneycare is basically a somewhat klutzy way of simulating single-payer. Instead of collecting enough revenue to pay for universal health insurance, it requires that those who can afford it buy the insurance directly, then provides aid -- financed with taxes -- to those who can't. The end result is much the same as if the government collected taxes from those under the mandate and bought insurance for them.
Yes, the system is surely less efficient than single-payer, both because it's more complex and because it introduces another layer of middlemen. That's what happens when you have to make political compromises. But it is in no sense more interventionist, more tyrannical, than Medicare; it's just a different way of achieving the same thing.