Actually, here's how it's going to go down.

Frank, not a day goes by where I do not think about killing them. It would be easy. I know how to do it. I have been trained to do it. I have no doubt that anyone else would do it. I cannot provide you with an argument that would convince you, because I do not have one myself. The only thing that keeps me from becoming you is irrational. It is a principle I hold, which I would understand you not to hold sacred.

But let me ask you this. I am willing to spend all of eternity in this room arguing with you. To me, you are just another man with a gun, one bullet away from blowing some boy's parents away. I do not care if history forgets me. I do not care if history forgets about Bruce Wayne. Villains will be brought to justice, if not by me, then by the people that I can entrust that task to.

But you. You don't have the luxury, do you? I am sure that you believe that, without you, your enemies will be allowed to live long, happy and disgusting lives. Relatively speaking, of course. I am sure that you believe that without the Punisher, the world's criminals would go unpunished. And I do not believe it is in your character to let that happen.

So, Frank, what will it be...? Should your enemies live long, happy lives outside bars? Or will you agree to my terms and never kill anyone again? I can provide you with the weapons and with the technology to make it possible. I am sure that you are resourceful enough to find different ways to make their lives miserable... And that, I can respect.

Frank Castle has agreed not to kill before, especially when working other Marvel heroes. I think that he can do that again if cosmic powers force him to, as long as it doesn't keep him from pursuing criminals. And with Batman's resources, I think that Frank Castle would realize that would also be a lot easier, perhaps more satisfying to accomplish.