Federal Mandates Have Been Around for over 200 Years
While everyone is arguing about whether Congress can compel everyone to buy a product (such as health insurance) from a private company, few people have noticed that the first time it did so was 220 years ago. On May 8, 1792, Congress passed the Second Militia Act, which ordered every able-bodied white male citizen from 18 to 45 to buy from a private company a musket or firelock and 24 rounds of ammunition for it. The full text of the act is given here: http://www.constitution.org/mil/mil_act_1792.htm
The United States had no standing army in 1792, so Congress was thinking that if the British came back, these armed men would form the militia to defend the country.
Congress did not state in the law which section of the constitution authorized this mandate. It could have been either Art. 1, Sec. 1, which gives it the power to raise armies, or conceivably the second amendment, which talks about a well-regulated militia and the right to bear arms. Nevertheless, the Second Militia Act was clearly a mandate forcing citizens to buy specific products from private companies at their own expense. Congress could, of course, have raised taxes and then authorized the President to buy the weapons with federal funds, distributing them to the militiamen in time of war, but it opted for a mandate instead. In any event, the idea of Congress mandating that citizens buy a specific product from a private company has a precedent that has gone unchallenged for 200 years.