"It's the quantity that is harmful, even water can be deadly if you drink it too much!"
Try drinking too much water. No one dies in the world because of drinking too much water willingly.
There are millions of drug addicts who die because they use too much heroin.
There are millions dying because they use too much sugar, alcohol, cigarettes...
Water is good for life. Sugar, alcohol, cigarettes, and drugs are bad. It is not about the quantity. A small amount of heroin doesn't make it good.
Stop deceiving yourself and parroting the propaganda of drug producers...