For the record, Ludwig Wittgenstein had already elucidated this point through logical analysis in Philosophical Investigations (1953).
Yglesias observes that in the view of Hillary Putnam, "The reason you can't rigidly separate positive from normative economics is that you can't rigidly separate claims of fact from claims of value in general. Human language is too laden with thick concepts that mix the two."
Read it at Slate
The Positive/Normative Distinction In Economics Is Nonsense But It Doesn't Really Matter
By Matthew Yglesias
I disagree with Matt that it doesn't really matter. It matters hugely, because obscuring the pervasiveness of the normative and prescriptive in economics and claiming that economic orthodoxy is positive while heterodox economics is not is central to the rhetoric of propaganda designed to justify neoliberalism.
Ravi Batra points out that in eras ruled by acquisitors, intellectuals prostitute themselves for fame, fortune and a share in power by justifying acquisitive behavior to laborers, who make up a vast majority of the population. They do this not through sound reasoning based on true premises and valid logical form, but by obscuring their intent behind a facade of sophistical rhetoric and displays of "expertise" designed to confuse the less-educated.
As Steve Keen artfully shows in Debunking Economics, neoliberalism rests on the "smoke" of sophistical assumptions and "mirrors" of complicated mathematical models that do not represent actual conditions. Thus, the premises are not as represented and the conclusions are also drawn by extending the application of the modeling beyond its scope in order to to convince the rubes that they are getting screwed for "scientific" reasons and there is no alternative other than the boogeyman of "socialism," which "everyone knows" ends in totalitarianism.
Yglesias says, "I think a lot of people who think they disagreement with most mainstream economists about certain things have noticed that most mainstream economists hold a somewhat naive metaphysical position and think that if they can debunk this metaphysical position they've vanquished the beast and now the doors are wide open to a utopia in which economists' critiques of their policy ideas have all been debunked. If mainstream economists are making a mistake in their analysis of the economy, you'll show that by engaging with their analysis of the economy not by engaging with their slipshod freelancing in metaphysics."
I think he is being naive here. The point of much economics is to justify a position that does not work economically, as the only alternative, for example, or the optimal solution.
TINA is often bolstered by the specious claim that every other approach leads to a socially unacceptable conclusion, like "socialism," or "totalitarianism." The focus on supply side is often justified on the basis of that this model of capitalism has generated a global system that has raised many out of poverty and produced the most advanced civilization to date, so let's leave well enough alone. These are specious arguments are successfully deployed to convine the "rabble" to vote against their own economic interests.
A bevy of think tanks have been funded by acquisitors to justify rapacity in the name of science. They are the go-to sources for the media and their manufactured credibility is used to justify propaganda. So, yes, the blending of fact and value, positive and normative, and descriptive and prescriptive is important and significant socially, politically, and economically in convincing the unsuspecting that their leaders are acting on the best scientific knowledge rather than self-serving ideology.