Overuse is then "proof" of the person's underlying problems.
That seems too reductive. Find me a person without "emotional / psychiatric problems"(!)
Substance use is multi-faceted. It can be modulated by availability (cost being a factor), social acceptability, religion, personal biology (eg alcohol intolerance), emotional state, age, physical addiction, history/habit, availability of substitutes (e.g. availability of heroin will tend to suppress use of krokodil), social supports and more.
To this way of thinking there was widespread heroin use among GIs in Vietnam because it was socially acceptable in context, widely available, people were bored, their usual social and emotional supports were not present, and for some, trauma.
You can change any of the factors above and that will influence how people use.