Believe it or not, the list of people Batman has killed is pretty long. Forget that the Dark Knight's supposed "one rule" is that he doesn't kill, he's actually a mass murdering maniac. This is especially true of his earliest adventures, which saw the vigilante brandishing and using a gun every chance he got. From mowing down villains to times Batman killed innocent people just to take the Joker down, there's no shortage of death at the hands of Batman. He might even have the biggest body count of all the DC superheroes.
The people Batman has murdered (be it outright or accidentally) includes the Joker, a vampire named the Monk, Dracula, and even Darkseid himself. He's shot people, burned them alive, hacked them to pieces, drained them of their blood, and hung them from the Batplane. It's a wonder this psychopath is still generally regarded as one of the best superheroes. Here are people Batman killed who didn't deserve it, so you can decide which end of the moral spectrum he truly falls on.
Legendary comic author Frank Miller is known for many things, but subtlety isn't one of them. Although he redefined Batman for a new generation with The Dark Knight Returns, his later Batman stories really suffered from a decidedly fascist take on the vigilante. Nowhere is this more obvious than in All-Star Batman and Robin, the Boy Wonder, which was drawn by Jim Lee.
Aside from Batman verbally and physically abusing a young Dick Grayson throughout the story, he also burns a group of criminals alive at one point for trying to steal a shipment of bleach (not kidding). Not only does he light them on fire with the same bleach they were trying to steal, Batman then proceeds to have sex with Black Canary a few feet away from where the men are burning to death.
DC's big Batman-centric series event, Dark Nights: Metal, imagines what would happen if the Dark Knight were pushed so far over the edge he just starts killing all of the bad guys. This series dedicates an entire multiverse to these nightmare versions of Batman. Whether driven mad by loss or defeated by one of his foes, the Batmen from the "Dark Multiverse" are twisted reimaginings of the already murderous Caped Crusader.
In one issue Batman snaps the Joker's neck but is infected with Joker toxin in the process. He then goes on a murder spree, killing off every member of his family and the Justice League. Though, actually, Batman kills off the Justice League in pretty much every one of the nightmare scenarios.
Dr. Hugo Strange, who debuted in Batman's earliest Detective Comics adventures, returned in the pages of Batman Vol. 1 #1 with an all-new master plan. Using a special growth serum, the mad scientist turns patients from an asylum into Monster Men - raging giants bent on destruction. When Batman gets word of this, he decides to get on the Batplane and stop Strange's henchmen from transporting one of the monsters to Gotham City.
Batman, who loves guns in his early days, uses a machine gun to shred through the henchmen's truck causing them to crash. Then he captures the Monster Man by tying a rope around his neck and hanging him from the Batplane. So yeah, Batman flies his fancy plane around with the corpse of his enemy suspended a few feet below.
In an alternate future, Bruce Wayne dies and his son, Damian, takes over as a new kind of Batman. A version, however, who has sold his soul to the Devil to keep Gotham City safe in a post-apocalyptic world covered in fire. A new villain known as "the Bat-Devil" arrives in Gotham claiming to be the Anti-Christ who will bring about Armageddon in the city. Damian goes to face the new bad guy. The Bat-Devil seriously underestimates Damian by thinking that he adheres to the same moral code as his dad, though. Damian makes short work of the Bat-Devil, cutting him open so that his guts spill out and then snapping his neck. It's probably the most gruesome murder in any of the Batmans' long history of killing.