The four liberals on the Supreme Court — Breyer, Ginsburg, Stevens, and Souter — all believe in an expansive version of Federal power. Presumably, all four also think that if sick people want to smoke pot and their doctorts agree, the Federal government should as a matter of policy, butt out. All four dutifully voted to uphold the Constitutionality of the Controlled Substances Act as applied to private noncommercial intrastate medical cannabis cultivation and possession.
The Court’s three hard-line conservatives — Rehnquist, Scalia, and Thomas — share a Constitutional doctrine placing greater restraint on the Federal government. But as social conservatives, all three presumably disapprove of smoking pot, even in a good cause. Nonetheless, two of them dutifully voted to strike down a law of which they, presumably, personally approved. (Having recently criticized Justice Thomas for voting his prejudices rather than his principles, I note with admiration his consistency in this instance.) Justice O’Connor, one of the swing Justices, writing in dissent, made the tension between her policy preferences and her Constitutional doctines explicit.
That leaves, of course, Justice Scalia, who gleefully struck down Federal power when it was used to protect women or keep guns away from schools, but voted to uphold it when it came to keeping medicine away from sick people. Is there any possible line of legal reasoning that could justify those three votes, taken together?
Volokh Conspirator Orin Kerr has lots of interesting doctrinal discussion about Raich, as does SCOTUSblog (start here and scroll down and down and down).