"Based on your posts in this thread, you appear to me to be an ultra-law and order guy."
I believe in the rule of law, yes.
"The morality of the law is irrelevant."
Do you think a law against addictive psychotropic recreational drugs is immoral? I don't. Why would you even bring that up in a thread like this?
"You appear to be a legal positivist"
You got that from what, one post?
I'll go with the Supreme Court's rulings in Lopez and Morrison. The Commerce Clause applies to anything that crosses the border of a State, into the United States, from an Indian reservation, is using a pathway for interstate commerce (an intrastate flight would apply here), or "substantially affects" interstate commerce.
How does smoking, or otherwise using, marijuana that's been grown and used in the same State "substantially affect" interstate commerce?