[sourcery]

Core paragraph from the Roberts opinion:

"Suppose Congress enacted a statute providing that every taxpayer who owns a house without energy efficient windows must pay $50 to the IRS. The amount due is adjusted based on factors such as taxable income and joint filing status, and is paid along with the taxpayer's income tax return. Those whose income is below the filing threshold need not pay. The required payment is not called a 'tax,' a 'penalty,' or anything else. No one would doubt that this law imposed a tax, and was within Congress’s power to tax. That conclusion should not change simply because Congress used the word 'penalty' to describe the payment. Interpreting such a law to be a tax would hardly '[i]mpos[e] a tax through judicial legislation.' Post, at 25. Rather, it would give practical effect to the Legislature’s enactment."

Now that I've studied the opinion, my interpretation is this:

Roberts argues two points (note: Not using these words--I'm extrapolating on my own):

1. The exact same effect as the "penalty" (fine) could have been achieved by using some combination of an income tax credit, increased income tax rates, reductions in the size of deductions, and even new filing statuses for "those without health insurance" (in addition to 'single,' 'married,' 'head of household,' etc) with different standard deductions and tax rates.
2. For Constitutional purposes, what something actually is is a function of what it actually does, not what it's called. So if it walks like a tax, talks like a tax, quacks like a tax, and acts like a tax, then it's a tax--or at least, based on past precedents, that's how it must be interpreted for the purpose of deciding Constitutionality if that's the only way to uphold a challenged law. And past precedents require that the Court must exercise every due diligence in order to find a way to interpret the law (but not the Constitution) so that the law may be found to be Constitutional.

So the argument is that since Congress could have achieved the same result--with precisely the same effects on everyone--by changing the income tax law, and since the assertion that X is a penalty is not the assertion that X cannot also be a tax (any tax may be intended as a penalty,) then interpreting the penalty as a tax is the interpretation of the law required by the Court's past precedents regarding how laws must be interpreted.

I will have more to say on this later.

[sourcery]

Here's more:

The fact that Roberts interpreted the mandate penalty as a tax does not mean he would rule it Constitutional, if a case came before the Court that persuasively made the argument that the mandate penalty-tax was not a Constitutionally-permissible tax.

In the context of the case that was before the Court, the only standard was whether the penalty could reasonably be seen as a tax under the taxing power, not whether such a tax was beyond any possibility of being successfully challenged Constitutionally. One reason for that is because the plaintiffs lacked standing to argue that point. To have standing on that issue, a plaintiff must first have paid the tax. Because of that, the Constitutionality of the tax as a tax was not a matter before the Court.

And that's one of the secrets to understanding court decisions.