Broadly speaking, I am pro-legalization of Pretty Much Everything, on the basis that proper education and appropriate treatment programs for heroin users are better for society than jail time.
But that comes with the need to implement pragmatic, evidence-based policies for how we approach drug use as a society.
A lot of neural development happens before your mid-20s, with a very large chunk happening during your adolescent years. Recreational drug use before your mid-20s, which includes alcohol and nicotine, really has a massive impact on your entire life.
I would argue that "soft" drugs, like low-percentage alcohol (beer and wine), maybe cocoa tea (not purified cocaine), and possibly low-percentage CBD should be relatively safe for adolescents from sixteen onwards.
Medical professionals, feel free to chime in if I'm wrong here. :)
Hard alcohol, nicotine, cocaine, and such, on the other hand, should have some access barrier for those under the age of twenty-five (90th percentile for complete neural development).
I wouldn't advocate an outright ban or criminalization -- if a teenager wants some weed and vodka, they're going to get it -- but putting some barriers in place to discourage consumption for the under-aged would be wise.
All of this, of course, needs to be coupled with comprehensive education.
The abstinence-only approach of "Just Say No" doesn't equip kids to really understand the full impact of the drugs they choose to use, and because of that, there's a lot of misinformation out there, ranging from "weed will make you crazy" to "it's completely safe for kids".
Neither of those things is true, and if we want to empower people to make good decisions, we must first be honest with them about the impact and trade-offs of the options on the table.
You still need a regulatory framework, and I would strongly argue for compulsory education on drug use, not to mention treatment programs, all of which should be funded through use taxes.
Otherwise, though, I agree very much with the libertarians that that empowering individuals to make their own life-choices is far more beneficial to society than criminalization and prohibition.
Without education, social support, and access to mental health care, a drug free-for-all could very well lead to such disastrous results that there is a backlash that returns us right back to criminalization and prohibition.
I mean, heavy use either way may be bad and boundaries are important with anything (weed, beer, chocolate, etc), but smoking the strongest stuff may be extra bad.