Even If The Individual Mandate Is A Tax, It's Still Unconstitutional
Chief Justice Roberts opinion on ObamaCare "should be studied for years to come as lesson of how a judge can reach his result no matter what the legal materials with which he is working," says Randy Barnett at Volokh. One of the weaknesses of Roberts opinion is his incredibly superficial treatment of the ramifications of treating the individual mandate as a tax.
For starters, what kind of tax is it? The Constitution grants Congress "Power To lay and collect Taxes, Duties, Imposts and Excises," however any "direct tax" must be apportioned so that each state pays in proportion to its income.
Rob Natelson explains that the original understanding "was that direct taxes were imposed on status, while indirect taxes were imposed on transactions. A tax that one must pay despite doing nothing is the quintessential direct tax." But if ObamaCare's "shared responsibility payment" (ie, the penalty for not buying insurance) is a direct tax, then it must fail since it is not apportioned.
The Chief Justice treated this question superficially, citing for example, a founding era case in which the justices "asserted or strongly suggested" that the only "direct taxes" were capitation taxes and land taxes. I think it's worth challenging Robert's assumption here, but such a challenge might have to wait until the government starts collecting the payment in 2014.