To make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this Constitution in the government of the United States, or in any department or officer thereof.

The Court went on to conclude that Congressional power over commerce should extend to the regulation of all aspects of it, overriding state law to the contrary:

If, as has always been understood, the sovereignty of Congress, though limited to specified objects, is plenary as to those objects, the power over commerce with foreign nations and among the several states is vested in Congress as absolutely as it would be in a single government, having in its constitution the same restrictions on the exercise of the power as are found in the Constitution of the United States.

[...]

Second: when people talk about judicial activism, one of the things they often say is: the Framers never imagined protecting X (or: making X illegal.) This, even if true, is irrelevant. What matters is construing the various meanings of the terms they used accurately, not matching up with their beliefs about what those terms apply to. My standard example: suppose that a law bans "carcinogens", and that some substance in common use when that law was enacted turns out, later, to be carcinogenic. This substance might then be banned, even though the legislators who enacted the law never anticipated that it would be. Would this show that "carcinogenic" had changed its meaning? No; just that we had discovered that it applies to something people didn't know it applied to when the law was passed. Someone who thought that this law should be read to ban only substances believed to be carcinogens when the law was passed would be a judicial activist: s/he would be trying to read a law that bans carcinogens as though it banned substances believed to be carcinogens at a given time. But if the legislators had intended to ban only those substances, they could perfectly well have said so.

It's easy to see that a law saying "no carcinogens" applies to all the things that are, in fact, carcinogens, and allows for future discoveries about the carcinogenic properties of apparently innocuous substances. But consider: are there similar discoveries about what "due process of law" requires? How would it be made? And how widely accepted would such a discovery have to be before it could be used to ground new due process rights? I don't think the answer to this question is clear *at all*. I am clear that saying "due process means whatever the Framers thought it meant" doesn't work: either it refers to the meaning (the "process of law" that is "due"), which is what's under debate, or else (Scalia version) it interprets "due process of law", as used by the Framers, to mean "those processes that we, the Framers, think count as 'due processes'", which it plainly does not mean. (If they had meant that, they could have said so.)

Likewise, in construing texts you often have to make assumptions about the intent of the author(s). Suppose the Constitution, or a law, refers to some right that makes no sense unless something else is presupposed: should you say that the Constitution/law holds that we ought to have that thing? (E.g., if it referred to a "right to vote" without stipulating that there had to be elections, and if it seemed plain from the text that the people who wrote it expected that there would be elections, would you say that the Constitution required it?) Likewise, is it generally a good principle of textual construction that an interpretation that makes the authors seem minimally sane and sensible is to be preferred to one that does not (e.g., that interpreting a document that refers to a "right to vote" as requiring the existence of elections is preferable to interpreting it as ensuring a right to vote, but as blithely unconcerned with whether or not any actual occasion to vote ever arises?) Arguably, yes: but people who don't like this will call it "judicial activism".

Here, the devil truly is in the details.