Snyder’ss Batman was the one pulling the trigger to take down crime. It’s assumed that if Batman, this protector of humanity, had to rely on a firearm, something he’d never done even when facing the Joker, an individual that killed his protege, then his departure into violence was fueled solely to eliminate the greatest threat to humanity.
However, and through empathy he realized that threat, an alien, was less of a threat than humanity itself. That even a god like creature cannot save humanity from their own primate brain. But accepting this alien creature as a man, and seeing the truth of his nature, it saved himself.
That’s why men are still good. It just wasn’t as expressly stated as in Wonder Woman. Man is worth saving. Despite our tribal tendencies.