I like your quote from Lao Tsu. I recently read the same assertion from C.G. Jung for why knowledge of good and evil go hand in hand. One cannot exist without the other because good and evil are values that we place upon things. Therefore, one cannot value good unless one also knows evil. It is why the mythical Jesus and the mythical devil go hand and hand in the Gospels because they are inextricably linked.
Right. Good and evil are relational, social, procedural. They emerge from a dynamic process of people being in the world and evaluating. Jesus and the devil are symbols of that but they're reified, as attempts to understand these relations or processes as things in themselves. Not that it's impossible to retrieve the esoteric meaning... anyways this is why I like the Dao. It's staunchly reification-proof.