Ah, but therein lies the rub! The regulation of interstate commerce is an enumerated power. The court, in Gonzales vs. Raich concluded that a product (in that case medical marijuana) that was privately grown for private consumption was never more than "one step away" from interstate commerce - and therefore the Federal Government could pass laws "necessary and proper" to prohibit sich growth.
Health Care is a "product" and, as such - never more than one step away from interstate commerce ....
Forcing citizens to enter into private contracts is a direct assault on what little remains of the Ninth.
The argument they are using is: "that a person's decision to not buy health insurance affects commerce by materially increasing the costs of others' health insurance."
When Gonzales vs. Raich was handed down, I substituted tomatoes to make a point - it applies here as well (and makes a mockery of this argument as it did the decision then): a person's decision to not buy tomatoes affects commerce by materially increasing the costs of others' tomatoes.
For instance, the Constitution of 1787 allowed for direct taxation. Congress could have passed a tax of $5 per person to pay the national debt at the time, for it was clearly necessary. Congress could NOT issue general warrants for federal tax collectors to enter each and every home in order to collect the tax because the IVth Amendment prohibits general warrants.
Even if Obamacare is necessary to implement an enumerated power (it isn't), it must be proper. That means it may not violate another portion of the Constitution, which it does, the Ninth Amendment.
It is a two fold test, both necessity and propriety are required.
Here is a thorough analysis of the necessary and proper clause by Randy Barnett.