Orin Kerr has an excellent one. Money quote:
Federal criminal law imposes a mandate upon any person who comes into innocent possession of child pornography. If a person comes into innocent possession of child pornography — for example, if you receive an unsolicited book in the mail, or an e-mail with an attachment, that contains child pornography — the law requires you to act to avoid criminal liability…[D]oes this law extend beyond Congress’s power by regulating inactivity?
The criminal law in question, 28 U.S.C. 2252(c), is enacted pursuant to Congress’s Commerce Clause power, and so, if (1) that power does not extend to regulations of inactivity and (2) receiving child pornography counts as inactivity then (3) 28 U.S.C. 2252(c) – as applied to those who receive child pornography – exceeds the constitutional limits on Congress’s power to regulate commerce. The proponents of the activity/inactivity distinction are committed to (1), so they must either deny (2) or embrace (3).
Hard to see how to deny (2) – receiving x [in the child porn case] and forgoing x [in the health care case] both seem to be examples of “inactivity” as it is construed by the proponents of the activity/inactivity distinction. This is because the activity/inactivity distinction is supposed to map, and be motivated by, the act/omission distinction. As Randy Barnett puts it in Commandeering the People:
At its root, the government’s ‘decision [to forgo health insurance] equals activity’ theory obliterates the well-known and intuitive distinction between acts and omissions. In the main, persons are responsible for their actions, not for their failure to act (p. 21).
As Barnett says, one of the act/omission distinction’s historical implications is that, absent a volitional act on your behalf, you owe no affirmative duties to others. But the law Kerr describes imposes an affirmative duty to act absent an initial volitional act, and so offends the act/omission distinction (and, thereby, the motivation for the activity/inactivity distinction).
The activity/inactivity distinction thus implies (3). This is certainly not a hurdle to libertarians accepting the activity/inactivity distinction, or to originalists accepting it, but it should make conservatives and those who don’t like overhauling entire swathes of the law – judicial minimalists? proponents of judicial restraint?…all these terms are contested – a little angsty.
Update: I think I might have been too hasty in endorsing Kerr’s hypo-reductio. 18 U.S.C. 2252(c) is
probably enacted pursuant to Congress’s power, identified in Perez v. United States, to regulate the misuse of interstate channels of commerce.* [I am wrong – Kerr indicates that language, added to the statute in 2007, about “affecting Congress” means it is supposed to be an extension of Congress’s power to its full constitutional limits.] This is a different power under the Commerce Clause than the power pursuant to which Congress enacted the ACA, viz. the power to regulate activities “substantially affecting” interstate commerce. Perhaps the activity/inactivity distinction only has relevance with respect to Congress’s power under the “substantial affects” line of Commerce Clause cases. The distinction is arguably inapposite with respect Congress’s power to regulate the “misuse of interstate channels of commerce,” because when the inactivity is, forgive me, a cataract in the stream of commerce it is thereby constitutive of interstate commerce and so reachable by the express terms of the Commerce Clause.
* “The Commerce Clause reaches, in the main, three categories of problems. First, the use of channels of interstate or foreign commerce which Congress deems are being misused, as, for example, the shipment of stolen goods  or of persons who have been kidnaped . Second, protection of the instrumentalities of interstate commerce, as for example, the destruction of an aircraft , or persons or things in commerce, as, for example, thefts from interstate shipments . Third, those activities affecting commerce.” Perez v. United States, 402 U.S. 146, 150 (1971)