In this case, a person who elects to pay the levy (to use a neutral term) rather than purchase insurance does all that the law requires him to do.

Having ruled that Congress had no power, under the Commerce Clause to impose an obligation to purchase insurance and a sanction for failing to do so, the only way in which the individual mandate could be upheld was by construing it as a tax.

To see this as embracing a “functional” view of law is misconceived; to hold that some laws are intended to impose an obligation, whilst some are not, is not functionalism.