A common meme, or idea taught to young children to stop them from trying different drugs. This is just another stereotype that is pushed on people. Drugs don't make people commit crime, drugs don't make people kill.
Drugs can make people bad, but it is close-minded to think that all drugs turn people into somebody worse than they originally were. Some drugs are used to calm people down, and reduce their violent tendencies. Some drugs are highly addictive, and cause people to commit crime to pay for more drugs. Other drugs make people hallucinate. Some drugs make people more aware of things around them. Other drugs make people vegetables, some cause people to become dependant on them. But used wisely, drugs can foster creativity, and a new state of mind.
Drugs themselves don't make people bad. The people weren't forced to use drugs, in the end it is their own personality flaws, the drugs only worsened their problems.