No, not true at all.
Supply and Demand.
The 'cost' of doing drugs in society right now is pretty dam high. Social stigma, the possibility of going to jail, various professional licences lost.
The 'free market price' of synthetic heroin and other drugs would be as cheap as sugar. Walk down to the local store and buy 1Kg of meth for $20. Jesus no.
People are really un-pragmatic about this issue.
I've had my exposure to it: a friend OD'd while in SF, another friend drug related suicide, and a third friend just fell in to a 'crack whole' for 20 years and now he lives full time in a clinic. Another - friend of a friend - has a 'weed' addiction (I know it's not common, but it exists) and he lives in a home as well.
These people were ruined long before they ever passed away or went into a home.
Selling crack or opioids in the corner store would instantly yield a massive public health crises.
'Legal' drugs - i.e. prescription drugs are already a major, major driver of the problem.
Here in Canada - doctors are not required to give out the 'absolute minimum' of opioids after operations etc. You don't get 'a bottle' with 'refills' - you get like 3 pills.
Why? Because there was a public healthcare crises developing even with legal substances.
That's how strict they need to be, because that's what's on the line.
If 'legal drugs' did not cause problems, then I suggest the massive amount of 'doctor shopping' and 'fake prescriptions' all over the US would not be resulting in serious problems, but they are.
It's just one of those things - some people can handle their drugs - most people can't and fall down the slippery slide.