" It is clear that spiritual naturalism can be used to defend any ‘positive’, i.e. existing, norm. For it can always be argued that these norms would not be in force if they did not express some traits of human nature. [...] In fact, this form of naturalism is so wide and so vague that it may be used to defend anything. There is nothing that has ever occurred to man which could not be claimed to be ‘natural’; for if it were not in his nature, how could it have occurred to him?

Looking back at this brief survey, we may perhaps discern two main tendencies which stand in the way of adopting a critical dualism. The first is a general tendency towards monism, that is to say, towards the reduction of norms to facts. The second lies deeper, and it possibly forms the background of the first. It is based upon our fear of admitting to ourselves that the responsibility for our ethical decisions is entirely ours and cannot be shifted to anybody else; neither to God, nor to nature, nor to society, nor to history. All these ethical theories attempt to find somebody, or perhaps some argument, to take the burden from us. But we cannot shirk this responsibility. Whatever authority we may accept, it is we who accept it. We only deceive ourselves if we do not realize this simple point. "

― Karl Popper , The Open Society and Its Enemies - Volume One: The Spell of Plato