This is the problem with a lack of character development, he said his power was forged in blood, but we never saw him kill anyone unjustly. In fact, he was only shown killing people that tried to kill him first, even forming a violent mob like the senators who killed Julius Caesar. It means nothing to the audience when he says his power was forged in blood, his words carry no weight, because we didn't experience his past with him, the author decided to cut all of it out of the story. It just seems like a pattern of cliches. Killing someone who attacks you should be common sense, and most people who have killed in self-defense, have been able to move on with their lives afterward.