See page about The Positivist Fallacy

I wrote a new page about The Positivist Fallacy which explains why positivism is impossible and the whole normative-positive distinction is illogical and useless at best or may even be harmful at worst.  An example of how positivism has been harmful is the rise of mmutilitarianism which happened when positivists helped motivate economics to reject its utilitarian moral foundation in the 1930s and 40s. This marriage of positivism and economics created a mutated accidental lovechild, mmutilitarianism, which would be less harmful if economists recognized it as being the moral philosophy that it is.  When you analyze mmutilitarianism using some of the other tools of moral philosophy, it is easy to intentionally use the strengths of mmutilitarian heuristics and avoid some of the weaknesses.