It doesn't matter to him that the states created that federal government in the first place, or how the people of those states, more than weary of the War On (Some) Drugs have voted. He says it's a matter of federal law and of various treaties that the government has signed (without our permission, by the way) with other governments. Any way you slice it, then it's all about the law, right?
Well, not exactly. Under what is probably the most commonly overlooked and criminally disregarded article of the Bill of Rights—the Ninth Amendment—Americans are entitled to do with their own bodies whatever the hell they damn well please. This fact was acknowledged, even by perverts who get their funsies controlling other people's lives, when the 20th century was relatively new and alcohol Prohibitionists found it necessary to amend the Constitution before they could outlaw booze. That law and that Amendment were repealed relatively quickly when it was finally pounded into the densest of Mrs. Grundian heads that Prohibition was doing vastly more damage to American society than alcohol ever had. It had made bottom-scrapings like Al Capone obscenely rich. And even worse, from the authoritarians' viewpoint, juries were stubbornly refusing to convict violators of Prohibition, humiliating the bucket-heads who supported it.
Drug laws and their inevitably violent and disruptive enforcement have done America similar (albeit far worse) damage, all in the name, and for the sake, of nothing more than employing thousands upon thousands, if not millions of otherwise unemployable goons, to play various Pushme-Pullyou games with politicos and gangsters and providing endless excuses to peer into people's private lives. But no such Constitutional Amendment was ever proposed or passed with regard to the broad range of substances we call "drugs", and so everything that government has ever done to interrupt the flow of drugs in underground (i.e., free) commerce is, itself, illegal.