Yes, but that is an example of how they determine the charges of something that is strictly illegal to begin with (in those states).

Controlled substances, on the other hand, are largely the result of federal legislation; technically--although there has been state defiance on marijuana laws-- generally, state laws can be stricter than federal laws but cannot be less strict. (i.e. even if a state doesn't criminalize something, they can't decriminalize something that is against federal law).

And surely Customs enforcement is federal-- the hurdle you would face in importation.

So I suppose you're right in a sense: states could criminalize this if they would like to, and the real question I'm asking is more about whether federal law would prohibit this.