From Rehnquist's majority opinion regarding indirect economic effect with relation to commerce clause.
In A. L. A. Schecter Poultry Corp.
v. United States
, 295 U.S. 495
, 550 (1935), the Court struck down regulations that fixed the hours and wages of individuals employed by an intrastate business because the activity being regulated related to interstate commerce only indirectly. In doing so, the Court characterized the distinction between direct and indirect effects of intrastate transactions upon interstate commerce as "a fundamental one, essential to the maintenance of our constitutional system." Id.
, at 548. Activities that affected interstate commerce directly were within Congress' power; activities that affected interstate commerce indirectly were beyond Congress' reach. Id., at 546. The justification for this formal distinction was rooted in the fear that otherwise "there would be virtually no limit to the federal power and for all practical purposes we should have a completely centralized government." Id., at 548.
And what you're quoting here is really strange: it's not at all the rule from the case. Rehnquist is giving a historical overview of the case law, here discussing a case, Schechter, that is largely no longer good law.
The "indirect affects" rule is dead. Since 1937 in fact.