Let's make an analogy with alcohol. When alcohol isn't illegal, there is a quality supply of it. When you buy a bottle of 40% whisky, you're not getting something that might be 25% methanol due to some criminal doing an improper job with the distilling, because he only cares about money, wiping out his competitors, and evading the cops, with your health being at the bottom of his priorities.

(Which is not to say, of course, that legal alcohol eliminates the public health problem of alcoholism.)