A Constitution of Convenience

This Washington Post editorial on the Raich decision exemplifies a mode of constitutional argument I invariably find irritating (also on display in Cass Sunstein's end of this Legal Affairs debate with Randy Barnett):

The plaintiffs in Raich, patients who regard pot as essential medication for their conditions, contended that because their use of the drug is noncommercial and within a single state that tolerates medical marijuana, the federal government lacked the power to stop them. This may seem like an attractive principle, but consider its implications. Can Congress protect an endangered species that exists only in a single state and may be wiped out by some noncommercial activity? Can it force an employer who operates only locally to accommodate the disabled?

Now, as it happens, I'm not terribly sympathetic to either of those policies in the instance. But even if I were, it surely wouldn't follow that the Constitution must empower the federal Congress to act in those cases, just because they're so awfully important. I am actually sympathetic to the idea that there ought to be federal regulation of pollution that isn't well constrained by state borders—I think the Constitution should've been (and should be) amended to grant it that power. That doesn't mean I think it must already have that power. Obviously, at some meta-level, your reading of the scope of constitutional rights and powers is going to be informed by some assessment of the consequences. I don't think it's reasonable to read the First Amendment as making laws against fraud or murder threats impermissible, even if some kind of hyper-literal construction might entail that. But if your notion of what the Constitution permits or forbids is just going to be guided by the sense that it would be a bad scene if Congress couldn't do something—note the total absence of a textual argument here, as if to say "it sure doesn't look like interstate commerce, but that doesn't matter"—well, why bother with enumerated powers (or a Constitution) at all?