I think God allows evil to exist because he gave us free will. Evil is just a consequence on having the power to decide our own fate. No free will, no evil; no evil, no free will.
Plants and animals don't have free will, so "evil" is a foreign concept to them. Predators can kill their prey for food, and monkeys can indiscriminately have *** with multiple partners (and relatives) without going to hell. But do we really want to live like them?
[ simon.cpu ]