If it is constitutional for the U.S. government to require you to purchase health insurance under penalty of law, then there is NO limit to what it require you to buy or to do.

David Harsanyi sums it up pretty well:

As U.S. District Court Judge Henry Hudson, who found the mandate unconstitutional recently, points out, "the same reasoning could apply to transportation, housing or nutritional decisions. This broad definition of the economic activity subject to congressional regulation lacks logical limitation."

Maybe that's the point. Force someone to buy a gun? Awful. Force someone to buy insurance? A victory for fairness. The limits of this philosophy depend solely on the subjective ideals and imaginations of powerful advocates.