The Punisher has been seen as both hero and villain. Many simply call him an anti-hero. He may be a killer but he is on a mission he feels is just. There's no denying that Frank Castle has suffered through the worst thing that could happen to a man. While living a normal life, he and his family stumbled across a gangland killing. To avoid having witness that could identify them, the killers attempted to do away with Frank, his wife and children. Luckily (or unluckily) Frank managed to survive. He forever has to live with the memory of seeing those he loved more than anything shot down before his eyes.
That day Frank Castle did die and the Punisher was born. He is now determined to rid the world of evil...to punish all those that commit evil acts. He feels it is now his duty to ensure the horrible incident he had to witness doesn't happen to others. There is is no discrimination when he sets his sights on this target. Criminal scum all have the potential to kill in some way and he believes the world will be better off without their existence.
But the Punisher is still human. No one is perfect. With the unpredictability of the gunfights he becomes part of, there's no way he can account for every possible scenario. He might do his best to ensure there is no one in harm's way but it would be impossible for him to be sure someone doesn't turn up at the wrong place at the wrong time. What if while having a shootout with criminals he accidentally shoots and kills and innocent bystander? Would the Punisher be able to live with himself if he killed someone that was innocent?
In the Ultimate Universe, this is something that does indeed happen. While convinced he was doing the right thing in protecting Nick Fury, the Punisher targeted Captain America (he wasn't gonna kill him, just shoot him in the kneecaps). Spider-Man saw this about to happen and did the only thing he could, he pushed Cap out of the way. This resulted in Spider-Man, an innocent teenager, getting shot (don't worry, he's not dead...yet).
Needless to say, the Punisher flipped out, demanding that he be punished for this.
While this was Mark Millar writing the Punisher in the Ultimate Universe, it raises the question of what would his reaction be? When I first read Ultimate Comics Avengers vs New Ultimates #4, I thought his reaction was a little extreme. It was almost comical.
The thing to consider is, we're talking about a man who could be considered either obsessed or crazy (or more likely both). His only mission is to rid the world of the bad guys and protect the innocent. By shooting an innocent, he becomes one of those bad guys.
This almost happened before. You've probably heard about the infamous Punisher Meets Archie comic. The premise is Punisher is after a druglord known as "Red" Fever. Punisher chases him to Riverdale. It turns out he looks almost identical to Archie Andrews.
Punisher could have easily accidentally shot Archie. Imagine how heartbroken Betty and Veronica would have been. Riverdale would never be the same and it would be all Punisher's fault.
I have to admit I have not read every single Punisher appearance. In the 90s alone he was appearing practically in every Marvel book. I'm a little surprised that there hasn't been any innocents caught in the crossfire. Has it happened and I've missed it. For the Punisher to shoot and kill an innocent, it would be devastating. I could see that really pushing him over the edge (over a different edge at least). He may be an expert marksman and tactician but nobody's perfect. There's bound to be innocents caught in his one-man war against the criminal scum. When that day happens, Frank is going to need some serious counseling.