It's recklessly naive to assume that legal status alone would prevent the vast majority of potential drug users from using drugs. It might matter to those on the fence, but those people, by and large, aren't going to turn out to be the type of drug users who turn into societal problems. And those drug users who are societal problems demonstrably could care less about their drug of choice's legal status.
In reality, laws are not a deterrent -- they're to protect persons from initiation of force. In reality, politicians and bureaucrats wield the power of government to create laws as a deterrent without regard to those laws initiating force, threat of force and/ fraud against persons and their property.
The federal government creates on average 3,000 new laws and regulations each year. Each state creates about a third that many. Almost everyone breaks the law several times each year, not including traffic laws. Surely with such profuse lawlessness persons and society should have self-destructed -- run headlong over a cliff edge long ago. But they haven't. Instead, persons and society have increasingly prospered in health wealth and well being.
Politicians, bureaucrats and other assorted parasitical elites, as well as patsies/stooges on this thread would have us believe that persons and society are always precariously perched on the precipice, just one step shy of plummeting to self-destruction.