Sure, if you are a big government authoritarian. Being able to attack people and extract property and money from them over a fucking highly-demanded weed is a gold mine for the state. Nevermind that outlawing a weed, makes it worth more than it's weight in gold. Get the CIA to sell that shit, along with crack and herion, and it's black budget paradise.
If you want to fill prisons with non-violent offenders so murderers and rapists can get out early, it's fucking great. Then you can use all that violence released back into society as a reason for even more tyrannical laws.
IOWs, unless you're a deepstate shill or a fucking moron, there is no reason it shouldn't be legalized.