that is not what the majority judgement says; it does not "make the original argument defacto unconstitutional" - that is not how decisions operate as this would mean a vast field of uncertainty in which unspoken implications were made law.
to avoid such total ambiguity in decisions, this would have been actually accomplished had the majority joined with roberts when he was making such assertions in section III-A, III-B and III-D. they did not. instead, the majority decision provides us, in sum, on the subject of commerce:
Code:
There may, however, be a more fundamental objection
to a tax on those who lack health insurance. Even if only
a tax, the payment under §5000A(b) remains a burden
that the Federal Government imposes for an omission, not
an act. If it is troubling to interpret the Commerce Clause
as authorizing Congress to regulate those who abstain
from commerce, perhaps it should be similarly troubling to
permit Congress to impose a tax for not doing something.
Three considerations allay this concern. First, and most
importantly, it is abundantly clear the Constitution does
not guarantee that individuals may avoid taxation through
inactivity. A capitation, after all, is a tax that every-
one must pay simply for existing, and capitations are
expressly contemplated by the Constitution. The Court
today holds that our Constitution protects us from federal
regulation under the Commerce Clause so long as we ab-
stain from the regulated activity. But from its creation,
the Constitution has made no such promise with respect to
taxes. See Letter from Benjamin Franklin to M. Le Roy
(Nov. 13, 1789) (“Our new Constitution is now established
. . . but in this world nothing can be said to be certain,
except death and taxes”).
Whether the mandate can be upheld under the Com-
merce Clause is a question about the scope of federal
authority. Its answer depends on whether Congress can
exercise what all acknowledge to be the novel course of
directing individuals to purchase insurance. Congress’s
use of the Taxing Clause to encourage buying something
is, by contrast, not new. Tax incentives already promote,
for example, purchasing homes and professional educa-
tions. See 26 U. S. C. §§163(h), 25A. Sustaining the
mandate as a tax depends only on whether Congress has
properly exercised its taxing power to encourage purchas-
ing health insurance, not whether it can. Upholding the
individual mandate under the Taxing Clause thus does
not recognize any new federal power. It determines that
Congress has used an existing one.
...
Third, although the breadth of Congress’s power to tax
is greater than its power to regulate commerce, the taxing
power does not give Congress the same degree of control
over individual behavior. Once we recognize that Con-
gress may regulate a particular decision under the Com-
merce Clause, the Federal Government can bring its full
weight to bear. Congress may simply command individ-
uals to do as it directs. An individual who disobeys may
be subjected to criminal sanctions. Those sanctions can
include not only fines and imprisonment, but all the at-
tendant consequences of being branded a criminal: depri-
vation of otherwise protected civil rights, such as the right
to bear arms or vote in elections; loss of employment op-
portunities; social stigma; and severe disabilities in other
controversies, such as custody or immigration disputes.
By contrast, Congress’s authority under the taxing
power is limited to requiring an individual to pay money
into the Federal Treasury, no more. If a tax is properly
paid, the Government has no power to compel or punish
individuals subject to it. We do not make light of the se-
vere burden that taxation—especially taxation motivated
by a regulatory purpose—can impose.
note that they explicitly do not answer "whether Congress can exercise what all acknowledge to be the novel course of directing individuals to purchase insurance", instead providing that the taxing power is sufficient.
thus the majority do not answer as to whether commerce/necessary and proper would be insufficient.
consider that roberts remarks in III-D that:
Code:
JUSTICE GINSBURG questions the necessity of rejecting
the Government’s commerce power argument, given that
§5000A can be upheld under the taxing power. Post, at 37.
But the statute reads more naturally as a command to buy
insurance than as a tax, and I would uphold it as a com-
mand if the Constitution allowed it. It is only because the
Commerce Clause does not authorize such a command
that it is necessary to reach the taxing power question.
And it is only because we have a duty to construe a stat-
ute to save it, if fairly possible, that §5000A can be inter-
preted as a tax. Without deciding the Commerce Clause
question, I would find no basis to adopt such a saving
construction.
this is the stance that you are essentially presenting, but we must recall that roberts was not joined in this section of the opinion, and was not joined in III-A and B, in which he explicitly 'decides the question', as you suggest would be performed "defacto".
this section is roberts' excuse for why he joined the majority even if he did not find support in commerce/necessary and proper - his opinion on commerce/necessary and proper remains separate from the majority judgement. judgements must be performed explicitly and the majority did not join this opinion!