"Spread of AIDS and other diseases, discarded syringes, overburdening social services, especially medical."
This doesn't fit the description of what I would consider a recreational user. You're talking about addicts of hard drugs, not occasional tokers.
Legalizing drugs legalizes all users -- proponents prefer to think in terms of the harmless, otherwise law-abiding, occassional, recreational user. But it would also be legal (and super-cheap) for the hardcore street addicts, and they would have an effect on public health.