For both conservatives and liberals, the answer seems to be a no-brainer. Of course it’s an assault on your liberty, say conservatives, for the government to compel you to buy a product in the private market that you wouldn't buy but for that compulsion. A government that can make you do that can take away the last shred of your economic liberty. Of course there's no encroachment on liberty, say liberals, since no one can possibly have a right to shift the cost of his health care onto others while refusing to bear his fair share of the cost of other people’s treatment. We routinely deny people permission to take a free ride on mutually advantageous social arrangements.
Jonathan Cohn has a good question for conservatives:
Again, let’s not get hung up on legalities. Social Security privatization and the individual mandate are constitutionally different inasmuch the former would be an exercise of the federal government’s taxing authority rather than its authority to regulate commerce among the states. But they present substantially the same question with respect to liberty.“You remember [Social Security] privatization, don’t you? The idea was to take Social Security, a mandatory public pension program, and turn it into a system of mandatory personal investment accounts. The schemes evolved over time, with different details, but the gist was always the same. During your working years, you’d make contributions into the accounts, just like you currently pay taxes that fill the Social Security Trust. Over time, you would invest the money in your private account—that is, you’d buy stocks, bonds, and so on—typically within certain guidelines set by the government. Once you hit retirement, you’d start to withdraw from the accounts or perhaps purchase an annuity, relying on subsequent payments for your financial security.
“Conservatives presumably thought privatization was constitutional; otherwise, they would not have worked so feverishly to enact it. But if the principle holds for old-age insurance, it ought to hold for medical insurance, too. In other words, if it’s ok for the government to make you pay for regulated private investments, then it should be ok for the government to make you pay for regulated private health insurance.”
Conservatives don't just think private Social Security accounts are consistent with the account-holder's liberty. They understandably think that they enhance it. As long you’re going to have a forced saving regime like Social Security, they reason, it's better that the people forced to save and subsidize other people's retirement have some control over how funds that go to their own retirement are invested and enjoy a real property right to the funds in their private accounts.
Well, we already have a system of public provision of health care in the sense that we don’t turn (Medicaid-ineligible) uninsured people away from tax-payer-supported hospital emergency rooms. And in our constitutional system, the federal government could use its taxing power to finance a single-payer system that would oblige every American to secure health care under the same terms and conditions. So why isn’t the individual mandate the liberty-enhancing choice in this menu of alternatives?