In James Tynion IV's Batman #99, Harley Quinn gives Batman something of an ultimatum. With the final showdown between Batman and the Joker at hand, she tells him that this battle between the old foes needs to end -- and she doesn't mean just the current one. Harley tells Batman that this ongoing war between them that has played out over years and years in Gotham finally needs to be over and there is only one ending that will work: the Joker has to die. As she says, it needs an ending and while one of the core values of Batman is that he does not kill, as we head into the final chapter of Joker War with this week's Batman #100 it's time to consider what feels like the unthinkable. It's time for Batman to kill the Joker.
While the idea that the Dark Knight would kill his greatest adversary is a shocking and perhaps controversial one, there are some fairly sound reasons as to why it needs to be done, but they largely boil down to one central theme: despite Batman's best and exhaustive efforts over many years, the Joker as a threat has not been contained and thus allowed the villain to not only do continued damage to Gotham, but, in a sense, undermines Batman's entire mission. Under that general umbrella, there are several reasons why Batman's continued unwillingness to do what needs to be done has created a situation in which he can never save Gotham -- and may even have in some sense made himself a part of the problem.
First up is the idea that the Joker cannot be rehabilitated because he's seen as mentally unstable, so there is no real justice to be had by apprehending him. If he's captured, being in Arkham does no good. He manages to escape every time and even when he doesn't escape right away, there's still rehabilitative value for his time there. If anything, he is able to expand his chaos in Arkham, completely making Batman's efforts moot.
There's also the idea that Batman doesn't kill, but there's also the idea that by not definitively ending the Joker, he's contributing to the villain's acts of death and destruction. Think of it this way: every single time Batman lets the Joker live, be that by the villain getting away or by Bruce having him locked up, he's all but guaranteeing that the Joker will be back. It happens every single time.
One could make a side note here that the reason Batman doesn't kill is that he sees all life as precious, including the Joker's, but that argument doesn't really hold water. If Batman really does see life as valuable, why is it okay for him to permit the Joker to kill countless others by virtue of being allowed to continue existing? The Joker kills and kills without rhyme or reason. By not putting an end to Joker, Batman is essentially saying that the lives of those the Joker kills matter less than calling into question what he really values.
That busts the "Batman doesn't kill" argument and its associated "Batman values life" claim.
But letting the Joker life is also not just about the lives the villain takes. The Joker's mayhem and schemes against Batman are escalating. The current Joker War arc is a shining example of that, with Joker going to a whole new level to mess with Batman. He takes his money, he exposes Bruce Wayne as "part of the problem" in Gotham, he turns all of Batman's assets and equipment against him and, in the process, undoes all of the good work he's been trying to accomplish in a city already reeling from City of Bane. By not putting a definitive stop to the Joker by ending his life, Batman is also undermining himself. You can't save a city that you choose to continue to let be destroyed.
It makes one wonder what Batman's real motives really are.
Realistically, on the pages of the Batman comic for all of the buildup and all of the hype, it's probable that the Joker is going to live to torment Batman another day. Even at the end of Batman #99, the Dark Knight is unwilling to accept the truth Harley is offering him. He's still determined to handle the Joker in his own way despite that way having been catastrophically ineffective for pretty much ever. But stepping back from the story of it all, it's past time for Batman to kill the Joker. The villain's continued existence has undermined Batman, made him complicit in his crimes, and put the Dark Knight in the position of being a hurt, not a help. If Batman truly wants to save Gotham, he needs to put an end to the biggest threat facing his beloved city. It's time for him to kill the Joker.