Batman turns every cell phone in Gotham into a microphone to find the Joker. It works. He finds him.
But Lucius Fox (The Ethics) threatens to resign. He knows that a tool built to catch a terrorist will eventually be used to control the citizens.
The Parallel: Homeland Security's new NYC Task Force. They say it's for "Transnational Gangs." History says it will be used against **You.**
After the Joker is caught, the machine self-destructs. Batman deletes the code.
This is the difference between a Hero and a Tyrant. A Hero uses power to solve the crisis and then **Gives It Up.** A Tyrant keeps the power "just in case."
Gotham didn't need Batman (The Vigilante). It needed Harvey Dent (The Law). But the Joker broke Harvey.
The system is fragile. When the "White Knight" falls, the "Dark Knight" must hold the line. We are in the Dark Knight phase.