My (novel?) defense of Obamacare's constitutionality

As reader(s)™ of the Blog know well, I am kind of obsessed with the constitutional challenge to the individual purchase requirement of Obamacare. I think I have a pretty good handle on all the arguments, pro and con. But today, as I pondered the eminent Ronald Dworkin's take on the subject, an argument in favor of its constitutionality occurred to me—an argument that I haven't seen anyone else make. Here it is, in its most distilled form:

1) The individual purchase requirement says that everyone (with some inconsequential exceptions) must purchase health insurance or pay a penalty that will be withheld from any income tax refund that would otherwise be due.

2) By its very terms, then, this requirement applies only to people who have earned income in the previous tax year. A person who earns no income, or even some income but not enough to create federal income tax liability, can choose not to buy health insurance without penalty.

3) Everyone who earns income has participated in interstate commerce (as that term of art is broadly defined under long-established Supreme Court cases such as Wickard v. Fillburn).

4) Therefore, the individual purchase requirement is an exercise of Congress's power to regulate interstate commerce because it is merely a condition imposed upon citizens who choose to participate in interstate commerce. No one who refrains from participating in interstate commerce is affected by the legislation.

Here are some objections that occur to me, with my counter-arguments:

• Where is the "limiting principle" to this argument? Answer: it requires participation in commerce that creates income. Response: But everyone participates in commerce that creates income. Reply: yes, exactly. This is what we have wrought. At least I am being honest about the doctrinal chain of command. And at least my argument requires participation in commerce, unlike standard defenses of the mandate, which embrace forcing people into commerce as a regulation of commerce.
• Isn't this just a tax? Answer: Pretty much. But I see it as the bridge between what's actually happening (a de facto tax) and what Congress said was happening (regulation of commerce).
• Isn't this just regulating people for breathing? Nope. Not unless they participate in commerce by earning income.
• Wouldn't this allow the federal government to imprison people for refusing to purchase health insurance? Answer: No; it might theoretically permit Congress to make it a crime for people who earn income to refuse to buy health insurance, but we don't have to decide that because that's not this case. In any event, it's already established that imprisoning people for home-growing marijuana is a valid exercise of the commerce power, and earning money seems a lot more inherently commercial than that.

What do you think, Mr. Gillette? Where's the weak point in my logic?