We all got trauma. Trauma isn’t what makes Batman interesting. Obsession is. The maniacal motivation to make himself into the greatest DCU superhero by sheer force of will.
Batman’s nuts. Like everybody else in Gotham. He’s pathologically obsessed with beating the crap out of criminals with his bare hands because he needs to emotionally. The fact that he’s saving the world is incidental.
That actually makes his “no killing” rule make more sense. A person doing this for moral reasons would grapple with the continuous living trolley problem embodied by The Joker, and would likely eventually do what needs to be done. An otherwise-decent person feeding addiction to violence would draw a hard line in the sand that he will never ever cross no matter the cost. Which sounds more like Bats?
It also makes his choice of weapons make more sense – tazers don’t satisfy him the way his fists do.
Yes he might also do philanthropic things but that’s not what drives him.
A hero driven by dark needs is way more interesting than a boring paragon of virtue.
It also gives his emotional divide from Nightwing a more coherent moral centre than just “Nightwing didn’t like how Batman’s mean”.