As has often been observed of the individual mandate, Congress had alternative means of achieving its end. (Congress could, for example, condition states’ receipt of federal funds on their cooperation in the gun-registration scheme.) The Constitution prohibits the states from doing many things, but only allows Congress to issue affirmative commands to the states in specified instances. This pattern implies the presumptive impropriety of additional commands.
The apparent point is to ensure, to the extent any constitution reasonably can, accountability. The constitutional baseline is that the federal government should not be able to blame the failure of its regulatory schemes on poor implementation by the states, and states should not be able to blame their administrative failures on unrealistic demands by the federal government. The Constitution cannot prevent governments from bargaining around this baseline to frustrate this goal, but it can force some transparency on the process.
In limiting commands from the federal government to individuals, the Constitution serves similar purposes. Congress cannot keep the costs of its ideas for health-care policy off the budget by simply ordering individuals to pick them up. Liberals have noted the supposed irony of the fact that a single-payer program would survive the constitutional scrutiny now being brought to bear on the mandate. The constitutional rule at issue nonetheless limits government by forcing Congress to confront the costs of any such scheme.