You are making a lot of assumptions about people in that situation. There are plenty of addicts who developed an addiction to opioids without ever taking an illegal substance. Maybe they are prescribed a pain killer after getting into a car accident and that eventually leads to oxycontin which leads to a heroine. Or maybe they experience some traumatic incident that leaves them with PTSD which interferes with their daily life and leads to drug use. No one can guarantee that neither of those situations will ever happen to them.