Why should the analysis of whether criminalizing the medicinal use of marijuana is a legitimate federal power turn on whether a state government has taken a view of the matter? If I follow your argument correctly, the federal government doesn’t have the power to prohibit medical marijuana–and it doesn’t have that power in Alabama, which also prohibits it, any more than it has it in California, which does not. If the federal law were an exercise of a legitimate power, on the other hand, a state could hardly nullify it within its borders. So the federal prohibition either is or isn’t within the federal government’s constitutional powers. Aren’t the state laws irrelevant to the question?
This is a good question, and one that took me some time to understand. For my answer, click here.