We should not will a world where killing is acceptable in to existencele in to existence  Knowing that we have agreed that there are situations where we can decide to kill others for the greater good makes us fearful of the prospect of others visiting such judgment on us (independent of whether such an act is objectively right or wrong). Immense psychological harm accrues from knowing that other people may actively judge oneself to be worth killing for an external purpose. Moreover, an acceptance of killing tends to brutalize society and make people more receptive to the idea of killing in general, which leads human beings to behave more violently.