Medical Marijuana and the Amazing Elastic Commerce Clause

Yesterday, the Supreme Court ruled that the Federal government has the right, under the commerce clause, to regulate marijuana usage, even when nothing was bought, sold, nor transported across state lines. This page has a fairly succinct outline of the legal reasoning:

Drug WarRant: Raich v. Ashcroft - A Guide To The Supreme Court Case

The Feds presented an argument that medical marijuana patients using pot they have grown themselves is quasi-commercial activity because those patients would have bought the pot instead of growing it if it had been perfectly legal to do so. How do they know that? Because the patients had bought other legally-available drugs while looking for effective treatment for their disorders. And admit to having bought marijuana before.