system
Given the following post, respond as if you're commenting on Reddit:
human
[Batman] What would Gotham be like if Batman suddenly started using lethal force?
gpt
Batman would quickly install a reign of terror and order in the city, ruling it with an iron fist and assuring peace and order in the city. Soon enough, with Gotham completely under his control, he turns his eyes towards the rest of the world. Bruce Wayne thus begins a comprehensive plan to take out criminals wherever they may be.

It is not long before the genius detective is attacked by other super heroes who do not believe in his new philosophy. Undeterred, Batman is always prepared and systematically takes them out as they try. As always, Batman refuses to change his mind or his course, regardless of what others think. He is a man on a mission. As Batman Inc. grows, it begins to work with small governments around the world to establish carefully controlled societies under strict vigilance. Anybody steps out of line and they are killed by Wayne Corp. sentinel drones.

Superheroes take not and start to seriously hunt him down. They don't succeed: Batman always has a plan. Unlike others, Batman wastes no time in killing them and removing the threat. No speeches, no nonsense. A kryptonite bullet, whatever it takes.

In short, Batman becomes one of DC Comics greatest supervillains. Woe to the earth if that happens. Do not underestimate the anger, the obsession and the desire for control that Batman feels. **He is a beast trapped in a cage of his own morals.** That invisible barrier is everything that keeps him on the side of the " good guys" . 
Why do you think he is so god damn strict? Of course he wants to kill the Joker and thinks that he should. He wants to kill all of them. Everyone. He wants to wipe them out, so that no little boy will ever again witness his parents get shot in a rat-infested alley somewhere. This is why Joker wants Batman to kill him so much : yes they have a personal war of ideological viewpoints and yes breaking the Batman down means Joker wins, but the punchline of that Joke is that by doing so , Joker will also unleash upon the world a horror that even he could never instill. And by one of its greatest heroes! Isn't that just....*hilarious?*