All drugs, at the moment, are illegal. So yes, criminals gravitate towards illegal drugs, because those are the only kind available, at least at the moment. :)
Unfortunately, due to keeping all drugs illegal, there is no reason for the pushers to ensure a safe supply. All they care about is keeping their customers as users.
However, if drugs of low dosage and addictiveness, enough to give you a buzz, were available, but regulated like alcohol, I think it’s reasonable to guess that 60% of those currently using drugs would be satisfied with that.
In areas like Anacostia there is no enforcement of drug laws. Drugs are dealt openly on the streets. Drugs are de facto legal in such places and are subject to observable market forces. What is quickly obvious is that people will buy the most effective drug that they can get for their money. There is little or no market for mild drugs with low addicitveness potential in Anacostia. Such a drug is already available in the form of Marijuana, but users go straight for the “good stuff” - crack, smack and speed. Legal mild drugs will not change the market.