Leo Tolstoy in The Kingdom of God is Within You:
"Besides, apologies for violence used against one's neighbor in defense of another neighbor from greater violence are always untrustworthy, because when force is used against one who has not yet carried out his evil intent, I can never know which would be greater--the evil of my act of violence or of the act I want to prevent. [...] I see that a man I know to be a ruffian is pursuing a young girl. I have a gun in my hand--I kill the ruffian and save the girl. But the death or the wounding of the ruffian has positively taken place, while what would have happened if this had not been I cannot know. And what an immense mass of evil must result, and indeed does result, from allowing men to assume the right of anticipating what might happen."