He'd become the Punisher if that's the case. I wouldn't mind if it's an alternate version if a really fucking dark and depressed and angry Bruce Wayne fighting crime using whatever means necessary to ensure the safety of Gotham and the world. I mean don't they do alternate versions of comic book characters like all the fucking time? I would laugh if they ever made Batman "KILLS" the DC Universe like it was done with The Punisher. Just leave regular Batman as he is though. A Rated R Dark Rough Brutal style as an alternate "what if" version only.
If you think about all these vigilantes like Batman, Spiderman and Daredevil etc do is beat the literal crap out of bad guys usually hospitalising them and then they are sent to jail only to escape the next day and go back on a crime spree. In the real world those criminals after recovering from hospital would be set free as there is no evidence to convict them and the vigilante would never take stand as a witness and would probably be arrested for assault and battery. Batman is more likely to cripple more criminals than he puts away. Whats the point of tge Gotham Police as tgey can't solve or do anything without Batman, everythime they see the Bat signal in the sky they must decide it coffee and donut time as obviously the caped crusader. I prefer the punishers brand of justice because unlike Batman if the punisher went up against the Joker then he wouldn't escape every month fron the insane asylum and go on a killing spree then caught and pummelled by batman for the 70th time.
Only in alternate universe storylines. The canonical batman doesn't lower himself to murder that often. Heroes are supposed to be better than that. They rise above their enemy they don't sink to their level.
The guy dresses like a bat, works in a cave, only goes out at night, and terrorizes criminals. To the public, everything about him seems sinister but the fact he never kills people proves he's not. That's why it's important.