Two economists are walking in the park. The first economist sees a pile of dog shit and says to the other, "I'll pay you $50 to eat that dog shit." So he does and gets paid $50. Later on, the second economist sees a pile of dog shit and says to the first, "I'll pay you $50 to eat that pile of dog shit." So he does and gets paid $50.

The first economist says, "I can't help but feel we just ate dog shit for nothing." "Nonsense," says the second economist, "We just contributed $100 to the economy."

Liberal economics is not a science but based on bad philosophy and assumptions about human psychology, dreamt up by "economists" with no background in psychology nor based on any empirical research, which have never been demonstrated in practice. Not only aren't they demonstrated, but they build mathematical models on top of these assumptions, but if the assumptions are meaningless, all the models are meaningless.

If you point this out, they will tell you, "sure, these assumptions aren't literally true, but they're just approximate." But in any rigorous science, if you approximate something, you're expected to calculate your error bars, so you can have an idea of just how approximate it is. If you don't, then for all you know, the error bars can be so big it has no relation to the real world. No liberal economist can tell you any way to actually determine how inaccurate their assumptions are, so you end up with a lot of maths, but none of it points back to anything real.

Conveniently, though, their maths just so happen to always work out to prove the conclusions they started with: free markets are inherently good, state controls are inherently bad. They have never updated their theories after witnessing their complete failure in eastern Europe, they in fact try to rewrite history to pretend like it was state controls that destroyed Russia's economy and free market anarchy that saved China's, which, as this video shows, the most basic overview of the facts shows to be the exact opposite of what happened.

—aimixin

Somebody else may be able to explain it better but the way I see it. Smith, Marx etc were venturing to describe an economic system that was just coming into being at the time (capitalism) and as such spent a lot of time engaging with the history of economic organization. They do a lot of work to arrive at how this system works (like, coming up with the labor theory of value and things like that) but are always conscious that all they’re doing is describing a system which is the result of the collective choices humans have made as a result of a historical (and Marx says dialectical) process with awareness of the fact that we can continue to reorganize society and evolve along that same process. Marx especially worked on developing the theory of how such historical progress might be made.

Economics, on the other hand, the way it’s taught and practiced now in capitalist society, takes this system as basically a law of nature. They talk about supply and demand curves like they’re describing the law of gravity. Some of the fundamental premises that all actors in the system are rational economic actors and that the market will self regulate to equilibrium and all this other stuff are basically false but taken for an almost religious truth. The whole industry of economics is set up to help capitalists make better decisions and predictions within this system using mathematical models with no mind paid toward whether these systems can and should be fundamentally reorganized to better meet the needs of society. They took the politics out of “political economy” to make a pseudo-mathematical discipline which they call economics. They mostly don’t content at all with Marx, they just pretend that his critique never existed. I’ve often thought of modern mainstream economists as fulfilling a role similar to the clergy in the old feudal system, existing to reinforce and justify the current order and the ruling class and propagate the ideology that benefits them. That may not be totally fair, I don’t want to say that economics is useless or that it doesn’t give us some good insight into how public policy can benefit people because obviously it does some of that too…. I’m kind of rambling, hope somebody else can jump in with a better or more concise explanation.

Here's another quick little joke about the fault in modern economics https://www.smbc-comics.com/comic/2013-01-14

Then there's some other stuff like how modern economics assumes we have infinite resources and everyone is a rational actor. These days they're being more "nuanced" in that they say they know these things are wrong, but they're good for modelling

There's a field called "nowcasting" which is the field of determining wether were in a recession at this moment.

Economics presents a lot of axioms and pretend these are built on absolute facts, when these things are neither so concrete as to be an axiom nor based on any real evidence.
Things like inflation being bad and the way to go against it is to give poor people less money.

If you don’t mind, could you expand on this?

Basically a bunch of French engineers started to develop an interest in the market theories that were going around in like 1890 and they started drawing weird curves and functions. Later they called it the "marginal revolution" and claimed to bring unbiased, rational, scientific thinking into economics. Of course this vibed well with neoliberalism, flash forward 100 years and now this shit is the ONLY economics we have left. Some math nerd in a terrible suit telling you you have to starve because "markets".

Here's a major proponent: https://en.m.wikipedia.org/wiki/L%C3%A9on_Walras