In light of a recent question of what a batman/spiderman type character could do the criminals he apprehends, how effective would this character be at preventing crime on a large scale?

I've always loved Batman/Rorschach type characters, but I wonder if in reality they would be as effective at stopping crime as they are in their stories. Do you think that these vigilantes would be an effective deterrent to crime? Or would they be dangerous/be ineffective in their pursuits? What do you think reddit?