IMO, It's more about the age than the drug.
There are substances that are legal to use. That's a fact.
People (the general public) have a right to do whatever they want to themselves, whether it helps or harms them (cigarettes, drugs, cutting, suicide).
As a Jew, one has an obligation to live, to not harm themselves.
When a jew gets a religious depression they turn to rebelling, whether public (change of friends and religious affiliation) or private (substances and religious observance).
If the jewish community come out against drugs full force they will only further the gap (case in point: Internet).
Rather let's accept the facts that substances exist and are accessible to all, but focus only having these questions with 20+ yr olds (which substances doesn't have great harm) rather than with 15 yr olds (where substances have a great harm).