Much of the discussion of the ruling has focused on the dissent by Antonin Scalia, who wrote:
The prohibition or deterrence of assisted suicide is certainly not among the enumerated powers conferred on the United States by the Constitution, and it is within the realm of public morality (bonos mores) traditionally addressed by the so-called police power of the States. But then, neither is prohibiting the recreational use of drugs or discouraging drug addiction among the enumerated powers. From an early time in our national history, the Federal Government has used its enumerated powers, such as its power to regulate interstate commerce, for the purpose of protecting public morality--for example, by banning the interstate shipment of lottery tickets, or the interstate transport of women for immoral purposes. ... Unless we are to repudiate a long and well-established principle of our jurisprudence, using the federal commerce power to prevent assisted suicide is unquestionably permissible. The question before us is not whether Congress can do this, or even whether Congress should do this; but simply whether Congress has done this in the CSA [Controlled Substances Act]. I think there is no doubt that it has. If the term "legitimate medical purpose" has any meaning, it surely excludes the prescription of drugs to produce death.
John Cole, Bill at INDC Journal, and Publius (among others) feel that this is a hypocritical position on Scalia's part, considering his invocation of federalism and state's rights and his opposition to Commerce Clause overreach in cases like United States v. Morrison. Baseball Crank at RedState.org disputes this charge:
This misunderstands the role of the Court and the role of enumerated powers. First, as Scalia noted, this is a long-settled doctrine, and nobody in the case was calling to overturn it. Even Justices who think that we may properly revisit long-settled Constitutional doctrines are usually hesitant to do so without any party to the case asking them to. All Scalia was doing here was assuming that Congress legitimately intended to legislate for this purpose, given 100+ years of history saying it could.
More to the point, there is a big difference between saying that Congress (or another branch of government) can go beyond its enumerated powers, and saying that Congress can act within those powers for unenumerated purposes. Here, we have the latter -- there is no question that the drugs involved in this case traveled in interstate commerce, and even Scalia is unlikely to sign on, at this late date, to a sufficiently cramped view of the commerce power to find that Congress can't regulate the use of goods shipped in interstate commerce; that battle was lost 70+ years ago.
As for the VAWA comparison, Crank writes:
... the Court in that case found an absence of proper basis for the commerce power in the first instance - i.e., an insufficient nexus between interstate commerce and domestic violence - rather than creating an affirmative rule repealing the commerce power, even when otherwise applicable, based upon the intended use of that power.
It is worth noting that the other regulated "immoral" activities Scalia cites actually do involve crossing state lines. By contrast, in physician-assisted suicide, the medicines cross state lines at some point, but their use occurs strictly within a single state. Using this kind of logic, one could argue that violence against women was a proper subject for congressional legislation under the Commerce Clause if either the victim or the perpetrator had crossed a state line at some point in their lives.
More to the point, the majority opinion by Justice Anthony Kennedy makes a very strong case that the CSA was intended to prohibit the illicit use of drugs related to addiction and recreational use, and not physician-assisted suicide. It may seem odd to describe assisted suicide as "legitimate" medicine, but it seems pretty clear that under the CSA "legitimate" means simply related to a medical purpose (rather than recreation, drug habit, or profit).
Do Scalia's own moral views influence his perception of what constitutes "legitimate medical purpose" or where the Commerce Clause may be legitimately applied? It's hard to avoid such a conclusion, considering that Scalia's opinions are so often colored by his personal views on such issues. Take Scalia's dissent in Lawrence: unlike Clarence Thomas, he did not simply argue that anti-sodomy laws were constitutionally permissible, but clearly didn't see anything particularly wrong with such laws.
Meanwhile, Thomas's separate dissent in Gonzales focuses on the contradiction between the majority opinion in this case and in Raich, the medical marijuana case, in which Thomas was also a dissenter. I agree with Thomas about the court's inconsistency (surely there is an irony somewhere in the Supreme Court saying that a state can't legalize medical marijuana but can legalize assisted suicide!), but it's disappointing that he chose to express his protest by writing an opinion that, in turn, is inconsistent with his own stance in Raich.