It's essentially a paradox between what is considered right and what is considered wrong. Does killing only criminals make you ultimately a good person? If you were a criminal, does killing other criminals some sort of cure-all penance for your own petty sins? It's all just one big morality lesson. Different people have different ideas on what is morally right and what is morally wrong. Good and evil does walk beside each other. Most people have their morality set with the rule that "killing people is wrong", but apparently, everything is justifiable if the person that is killed is a killer [him/her]self. The ends justify the means; a principle that humanity knows far too well and is the difference between humanity and all other species on this planet.