“a tax on inactivity does not fall within the prescribed functions for which taxes may be levied”
It is not so much a tax on nonaction as on the status of not possessing insurance. Which makes it akin to all manner of direct taxes, for instance the tax on having earned so much income in the last year or a tax on ownersio of property.
“nor the forms of taxes permitted.”
True. If it us a direct tax, and it is, it must be apportioned. If it is an income tax, which it isn’t, it wouldn’t need to. But it isn’t, so it doesn’t.
It’s exactly a “tax” on inactivity. (Actually, it’s not a tax at all — it’s a penalty.)