Would it also be a state's right to legalize it for ANY use? Marijuana is a controlled substance, just like tobacco, alcohol, and firearms...
The cleanest answer would be to get a federal law stating that it would be a state decision. Barring that, you would have to craft the state law to strictly ban the transport of marijuana across state lines.
The Federal government usually steps in if it can claim that interstate commerce is involved.
The biggest problem I have with the whole legalization argument is this: Where do you stop? Ok, fine, many people think that Marijuana is a relatively harmless drug. I don’t believe this, but I will concede the point for argument’s sake. Do you then, also legalize heroine? How about meth? Crack cocaine? Some substances are so dangerous, I don’t see how they can be legalized. Drugs are a scourge on American society, including the overuse of legal prescription medications. Hard drugs are even worse than alcohol in the destruction they bring to one’s health and social order. Yes, legalizing drugs would remove a lot of the criminal element associated with the drug trade, but not completely. Criminal gangs would just manufacture or import even more destructive drugs to replace that revenue stream. So, where does it stop? I would like the country to be more socially conservative like the 1950’s and less like Haight-Ashbury. I don’t see how adding one more legal drug to the already extensive list of legal drugs available accomplishes that personal wish.
If people decide through the electoral process to legalize a drug(s), so be it. However, overall, I don’t this will do anything to make our society better or make us any more competitive in world trade, quite the opposite IMHO.