It is the price. Not many people addicted to cheap legal drugs become criminals. To buy cigarettes or grog, it is enough to work a low-paying job or just beg for money. Personally, i don't believe you should be able to buy hard drugs in the supermarket, but there should be a cheap legal way to buy them from a doctor and get help at the same time.

It's part of a strong argument for making them illegal. You'd also need to show that making them illegal actually decreases the rate at which that happens.