It would have to be with the second part of that same sentence, "which viewed in the aggregate, substantially affects interstate commerce."
One person, no effect. But looking at the aggregate effect, it's obvious the courts feel there is a "substantial effect" on interstate commerce. My own opinion? It's a stretch, but valid.
Everyone is losing sight of one key ingredient here -- Conngress must first pass a law. People are getting hung up on how the commerce clause is being interpreted (or misinterpreted) as if that's where the "problem" is. Congress can't just willy-nilly start regulating gardens, and apples, and whatever. That law has to pass both houses and be signed by the President. Then it has to survive court challenges to "essential part" and "substantial effects" -- some do, some don't.
The "problem", for those whose wish to legalize marijuana, is the law, not the commerce clause. Placing the blame on the Supreme Court diverts your attention from the real reason that marijuana is illegal: The voters want marijuana to be illegal.
Unfortunately the second part of that sentence does not stand alone, but is dependent on the first part, which specifies "activities that arise out of or are connected with a commercial transaction".
In terms of the explosive growth of the federal government, and it's intrusion into areas of our lives it shouldn't be concerned with, it is the problem, or at least the part of the problem we can deal with without getting into legislating mind control.