Frank believes the system is hopelessly broken. so he has to be above it and take out everyone himself. Nothing will ever actually get better and he's ultimately fighting an unwinnable battle.
Bruce believes the system can be saved. if he helps catch criminals then trials and such take care of the rest. people begin to believe that society can work, and Gotham becomes a better city. (of course they don't in comics world because villains arbitrarily walk back out for the next lazy writer)
So Bats had hope but it's based on real world ideals, not coming world. While PunPun Killchan is a homicidal maniac but for better in context