That is the primary argument against legalization / decriminalization. MJ legalization has led to a 20% increase in use already. It's a very good argument.
The only argument I have for legalization is the current situation we have with Mexico (and Guatemala, etc). Our inability to not control/treat drug addiction has led to a fundamentally destabilized country in a de facto civil war (against cartels we trained in the School of the Americas, an entirely different nutso side). Those cartels are supported by the economics of illegal drugs.
Not just that, with the fall of our puppet regime in Afghanistan, we will be enriching the Taliban regime by paying for the output of their poppy fields.
What is mindblowing is listening to all my right leaning relatives scream at the top of their lungs about the illegal immigration flood, but they are the ones supporting the side that most opposes dealing with the drug problem in a constructive way.
IMO the fundamental way to fight illegal drugs is to decriminalize, replace the supply / undermine the economics with medically or governmentally supply (at prices that undercut mafia economics), and make treatment zero-cost available as part of the drug availability.
Of course that will probably lead to something like Purdue Pharma and painkillers / Medicaid fraud.
But the War on Drugs has to end.
