First of all, smoking marijuana is not illegal. Possessing it is. Taken collectively, possessing marijuana has a substantial effect on interstate commerce.
No different than flying your private airplane within your state. The moment you start having a substantial effect on interstate air traffic (ie., flying within controlled airspace), Congress (via the FAA) may regulate your in-state activity.
Or are you saying that since your flying is not interstate and is not even commerce, that Congress has no right to intervene?
Based on your posts in this thread, you appear to me to be an ultra-law and order guy. The law says marijuana is illegal, end of discussion. If marijuana was legalized, then you would have no problem with marijuana. The morality of the law is irrelevant. All that matters is what the law says. You appear to be a legal positivist. Please correct me if I’m wrong.