The answer to your question is because God gave us free will. How exactly would life work if we were all pre-programmed and didn't have the capacity to make decisions. Within that framework, people make mistakes and have the ability to learn and modify their behavior. And quite frankly, as an atheist, who are you to judge good and evil? At the base of your beliefs, all humans are just a bunch of animals and one person harming another is no different than watching a couple ants battle it out. And why are you so angry against Christianity? You sound like Bill Maher😂