Looking from the outside, US constitutional law has always seemed like this absurd tangle of kabbalistic reinterpretations, but it seems important to mention that AFAIK the federal ban on child labour (whether or not its products cross state lines) rests on similarly twisty reasoning. (Things like environmental protections as well, probably, but this looks to have been the first example.) “Let’s allow the federal government to regulate whatever” is a value-neutral weapon.

Clarence Thomas actually dissented on this and said it was crazy.