Of course. But here's what we can reduce by relegalizing: deaths of innocents in drug-turf wars; deaths of users due to impurities or unexpectedly high potencies; enrichment of criminals; corruption of the justice system by enriched criminals; and lessened respect for the law in general.
smoking, drinking alcohol, gambling, eating fast food
Going by your rationalization, these should be outlawed as well. But when eating fast food is outlawed, only outlaws will eat fast food.