Your statement assumes that drug prohibitions exist to protect the health of the public. This is, as you've pointed out, demonstrably false. If, on the other hand, you view drug laws as a means to criminalize a large percentage of the population and give police a ton of discretion in declaring who is and isn't a criminal, the situation become entirely consistent and you realize that drug laws are nothing more than a way to keep prisons full and allow police to remove "undesirables" (read: minorities) from society.
Allowing the the drug war to be framed as a public health issue means arguing on terms chosen by proponents of the drug war. We need to reject that premise and discuss it for what it really is, a racially-motivated tool for social repression. If those that argue against what you suggest (safe an legal avenues for drug use) were forced to show that, absent the current drug laws, the damage to society would be greater than the damage inflicted by the drug laws themselves, their arguments would look even more foolish than they currently appear.