Basically, nobody knows anything. But if everyone were to admit that, there would be no basis on which to conduct policy. → Chaos/arbitrariness/incoherence (over time and sectors)
So people make up and promote a narrative (bullshit story) and if enough people believe / are made to believe in it, then you have a basis for relatively stable and coherent policy regime.
This interpretation of economics (as a field) is consistent with the history of economic ideas. No economic ideas are ever discarded or disproven (the very antithesis of science if you will). As the Economist aptly put it: "Macroeconomic arguments tend not to produce winners and losers: only those with more in- fluence and those with less."
That's why economics (the field) is really less about economics (the substance) but about politics and power.
 Hyperbolically speaking, of course, and aimed in particular at macro- and monetary economists. There are some nice results but they apply, as far as I could tell, mostly to smaller settings, not the aggregate economy.
 The Economist. Free exchange: Magic or logic? page 69, Mar 16 2019.
In a situation that affects so many people, it may seem unwise to do experiments and try things where we can not say with certainty what effects they might have, though we admit they may be substantial. The ethics are very dim on that front. But the alternative has to be considered. We do not have 'generally accepted treatment' to turn to and rely on. We only have other experiments, albeit while not calling them experiments and not treating them as if their outcomes are in doubt, simply forging ahead with blinders on. I can't imagine an argument that would justify that as more ethical than earnestly doing experiments.
This is analogous to why econometrics is bullshit: lack of stationarity in the real world.
This is amplified by nonlinearities in the system. So even if things today were broadly comparable to, say, the 1990s (and they're emphatically not), what if there was this little thing somewhere (like an obscure accounting regulation) that led to massive differences in the outcome of the experiment?
Tbc, I think there are better and worse ways to deal with the problem, just because we know so little does not mean everything is equally meaningless.