So the Tenth Amendment isn't enough to persuade you?
Sure, but only if I can first be persuaded that Marijuana cannot pose the sort of threat that Opium or Cocaine poses. I regard some of the harder drugs to be existential (Threatening our very existence) threats to our nation. I have read quite a lot about what Opium did to China, and I am convinced it was the breakdown in society which was caused by Opium addiction that led first to the Japanese invasion of China, and thereafter to the ascendency of the Communist Mao government with it's 100 million subsequent deaths.
Now could Marijuana trigger such an event here? If the answer is yes, then the 10th amendment cannot protect it. If the answer is no, then allowing it would seemingly fall within the tenth Amendment's purview.
The question I am not certain of in my own mind is which side of the line is Marijuana on? Would ubiquitous society-wide usage of the drug destroy our ability to maintain a functioning nation? I don't know. I know it makes worthless lazy bums out of the people I know who use it, but presumably it may not have that effect on everyone.
I would suggest that Licensing it's usage would address this issue. It would establish the idea that the State has a right to regulate it (Under the State's tenth amendment powers) and that it is being watched closely enough to guarantee that any unintended consequences can be ameliorated by tightening the requirements for licensing.
For that matter, I think consumers of Alcohol ought to have a box on their drivers license that can be checked to verify that they have been advised of their rights and responsibilities, and which can be unchecked for people convicted of drunk driving or other abuses of the substance.
It would keep the sales and use of it legal, while reducing traffic accidents by repeat offenders. (I know a guy with 5 D.U.I.s and another with 7 D.U.I.s.) Bartenders could ask to see their license (which they often do anyways) and if they don't have that box checked, they can be refused service.
But getting back to Marijuana, the question is just how much of a threat to a functioning society is Marijuana? I don't know. I would suggest the best way to figure this out is to look at societies that have already legalized it and see what kind of bad consequences resulted.
People claim that Portugal is having success with this approach, but there are dissenters who claim the Portuguese government is just making up their claims of success. People often cite Amsterdam Netherlands as an example of successful integration of Marijuana and Society, but the latest news from that Country is that they are now banning it's sale or use by Foreign Tourists.
From my perspective, it's still an open question, though I would think allowing licenses for it would address my strongest concerns.