Is it? The Constitution grants Congress only four areas in which taxes can be levied: excise, impost, direct and income. Nowhere does it allow taxation for a negative action. This tax is nothing less than a tax on liberty.
Should the law stand, I expect that argument to be made in the courts, but they can’t make it yet until they actually start collecting the tax. I suspect this is why Ginsburg was so upset. Roberts might have screwed them royally.