Why should the knowledge of good and evil be forbidden?

There is no knowledge of good and evil in the wild. It is an entirely spiritual thing. The Bible's myth of the Fall of Adam, whereby humans acquire the knowledge of good and evil, represents the evolution of human beings from natural creatures who do not sin into spiritual creatures who do. Its moral point seems to be that the awful knowledge of good and evil entailed by being human, called the human condition, is a terrible and often unbearable burden for us. By forbidding it, God was doing us a favor. We were happier without it.