If you murder a murderer, you don't reduce the total number of murderers. You have to murder more than one, but then you're a serial killer, which is arguably worse. If you're a serial killer who only kills serial killers, then you are starting to maximize the offset. But once you fuck up and get close to being caught, so your serial killer girlfriend blows up Doakes to keep your secret safe and you pin all your murders on him, you've gone too far.
Yeah but how do you know the murderer you murdered wasn't just murdering other murderers like your murderering MO? You could still have a net sum of 0 murderers removed from society🫠
I learned from the new Dexter show that you have to kill three times to become a serial killer. So, it seems like two is the optimum number here, reducing the number of murderers by one and increasing the number of serial killers by none.