First the drafters of the Affordable Care Act failed to include  a"severability" clause, which would ensure that if any portion of it was ruled unconstitutional, the rest would remain in effect. Fortunately, judge Henry Hudson's ruling against the individual mandate didn't endeavor to toss out the entire law. It did, however, seem to be premised entirely on a simple misreading of the Constitution:

The key portion of the ruling reads:
"If a person's decision not to purchase health insurance at a particular point in time does not constitute the type of economic activity subject to regulation under the Commerce Clause, then logically an attempt to enforce such provision under the Necessary and Proper Clause is equally offensive to the Constitution."
[GWU law professor Orin] Kerr notes that this is all wrong. The Necessary and Proper Clause allows Congress to take steps beyond those listed in the Constitution to achieve its Constitutional ends, including the regulation of interstate commerce. Hudson's argument wipes a key part of the Constitution out of existence. Kerr says Hudson "rendered [it] a nullity."
Kerr's co-blogger, Case Western Reserve University Law Professor Jonathan Adler agreed, though he cautioned that Hudson's error doesn't necessarily imply that the mandate is constitutional.
In an interview with TPM this morning, Timothy Jost of Washington and Lee University, a supporter of the mandate, called the logic on this point "completely redundant."
"In Hudson's opinion he basically conflates the Commerce power and the Necessary and Proper power and says that each provision in a statute has to be looked at independently from every other provision, and each provision has to be independently authorized under the Commerce Clause," Jost said. "And if it isn't, the Necessary and Proper Clause doesn't grant any more authority."

Even in the context of concocting arguments that the Constitution forbids Congress from enacting policies that you hate, this seems remarkably inept.