Shi Po Tian has 2 principles he holds strongly to right from the beginning of his story. One is 'no begging', the other is 'cannot kill humans'. Readers are told that the 'no begging' principle was beaten into him by his foster mother. The 'cannot kill humans' principle, he learned from stories his mother told him when she's in a good mood.
I wonder what stories she told him that made him hold this principle so strongly. I believe ancient tales contains many stories of killings, right? Heroes killing bad people. Warrior killing the enemies. So, how come he's so against killing? He's not only against killing good guys, bad guys also he doesn't want to kill.
But then when his sworn brother Zhang Shan killed, he didn't seem upset. He was just awed by his awesome martial arts. When Zhang Shan led/forced the Iron Fork members all into the poisonous chamber, he called out to the guys not to go in and wondered why Zhang Shan did that. But he didn't seem upset. Just confused.