This is exactly the answer. It's also the reason for perennial disputes about states rights, and the exact reason that the constitution was written the way it was - all rights not specifically enumerated lie with the states. Unfortunately, the interstate commerce clause has become the mother of all loopholes, and the federal government has ballooned to be an order of magnitude (at least) larger than it was ever intended to be. And now it wields all this unintended power and collects copious amounts of tax revenue, which it then turns around and wields against the states to exercise yet more power.