In American comics, every superhero had to have a supervillain nemesis, and those villains all had more or less some psychological problems.
Take Batman's enemy, the "Joker." He was practically synonymous with chaos and mental instability. Yet under the Durham Rule, as long as there was a clinical diagnosis as the "result," someone with his kind of mental illness could be acquitted, only to be locked in a psychiatric hospital for life.
Yet even mentally ill people were not constantly insane, crazed, or confused to the point of not knowing their own names or families. They also had lucid, rational moments. If someone truly suffered from permanent mental disorder, they would not have the capacity to commit crimes in the first place.
If someone in Britain used mental disorder as a defense for acquittal, unless they had sufficient evidence proving that they had suffered an episode when committing the crime, it would be difficult to obtain a not-guilty verdict from the jury.
Even mentally ill people could improve with proper treatment. But the city where Arthur lived was on strike, and the mayor had spent the money meant for patients' medicine on police overtime pay. This made his condition worse. Then he suffered a series of blows—losing his job, his mother's death, and more. He had nothing left to lose.
Then he got a gun. Unlike other supervillains, he had no superpowers, but the destruction he caused was just as astonishing.
The whole of Gotham was engulfed in flames, with destruction and chaos everywhere. After being arrested, the Joker actually said the scene was beautiful.
Life was unequal. Not everyone was like Batman, with a wealthy father and a technology company building Batmobiles for him.
When Batman drove that car to chase criminals, he sometimes broke traffic laws and even