In fairness, the story about her killing Lord was done with a lot more nuance (people forget she actually begged Lord not to go through with his plan before making the decision to kill him). It was Geoff Johns during Infinite Crisis that depicted her as the most murderous of the Trinity (not that Superman or Batman was anymore sympathetic during that story). And her killing Max doesn't have to make her look so monstrous. She killed people in her debut movie and most didn't have an issue with that. Diana killing isn't a problem, so much as the context.