I think legalisation ought to be driven largely evidence of harm, not just by abuse of the drugs, but systemic harm both of legalisation vs. criminalization, but with a reasonably high level of ability to take personal risk.

E.g. for drugs where we know addiction drives crime, even fairly substantial harm from the drug itself might still mean legalisation is a net gain. Heroin might fit in that bucket (a small UK trial with prescribing it saw offending rates for those in the trial drop dramatically, and so reducing net harm to society).

At the same time high risk may justify a high degree of regulation of specific drugs to ensure people are at least aware of the dangers, and aim to reduce recruitment.