Er, what? If you fund or help fund a criminal enterprise, you can be prosecuted for it. If someone was funnelling millions of dollars to, say, a child sex slave ring, you think that the constitution protects their sending of that money and they can't be charged for it?
I don't personally think drugs should be illegal at all, but I do think that funding crimes in general should be illegal, which is essentially what Shrem was charged with here.