From page 42 of the ruling by Judge  Roger Vinson:

It would be a radical departure from existing case law to hold that Congress can regulate inactivity under the Commerce Clause. If it has the power to compelan otherwise passive individual into a commercial transaction with a third party merely by asserting — as was done in the Act — that compelling the actual transaction is itself “commercial and economic in nature, and substantially affects interstate commerce” [see Act § 1501(a)(1)], it is not hyperbolizing to suggest that Congress could do almost anything it wanted. It is difficult to imagine that a nation which began, at least in part, as the result of opposition to a British mandate giving the East India Company a monopoly and imposing a nominal tax on all tea sold in America would have set out to create a government with the power to force people to buy tea in the first place. If Congress can penalize a passive individual for failing to engage in commerce, the enumeration of powers in the Constitution would have been in vain for it would be “difficult to perceive any limitation on federal power”[Lopez, supra, 514 U.S. at 564], and we would have a Constitution in name only.