Well there was a guy with a funny beard who wrote about what happens when capitalism produces more goods and services than could ever be reasonably consumed by the populace of the world. He wrote about how there were basically 2 coutcomes. Either the the rising supply just keeps pushing prices down until the only issue comes down to a logistics and distribution problem and money functionally becomes pointless and state power doesnt have any heirarchy to enforce. Or the people with money and power enforce artificial scarcity, through tactics like letting crops die in the fields, or only release so many diamonds into the market and promiting it as a good thing, to protect their wealth and power.

We've used every economic system by itself

Because a few hundred years with constantly changing technology is an exhaustive test of every possible version of organizing society. Pack up folks, it's all been tried and only one thing works or will ever work.

The biggest issue is that this is a doomer self defeating argument. If you don't believe something is possible, then it isn't. Even if total communism is an unreachable goal, why not try to move closer to it? Liberalism is a walking contradiction, with economic liberalism being almost incompatible with social liberalism. That hasn't stopped it from having drastic positive and negative effects on human history from people trying to live by it.

Furthermore, the idea that communism is a dead end reinforces the toxic view that anyone attempting to strive closer towards it is a threat that must be eliminated. Anti-communist sentiment has led to and enabled some of the worst atrocities of all time. The best part is that many of the people accused of being communists merely wanted liberation.

The fact is, if communism was wiped from existence and Karl Marx erased from history, the same ideas would evolve out of Christianity, or liberalism, or any ideology that isn't a fucking death cult. This is because Marx did not make a unique and unprecedented observation, he just put the pieces together first. Egalitarianism and sharing is as important to human success as territorialism and self interest.

Finally, Marx did believe communism would come out of industrialized societies with enough resources to go around. That is not the state that the Soviet Union or China were in when they declared themselves communist. Making absolute statements about the end state of all attempts at something is setting yourself up for failure far more than trying a new way to make something theoretically possible happen.

I think it's pretty clear we aren't necessarily talking only about the quantity of bills passed, but also the quality

This (please don't stone me for just saying a word, but I tried to express this point in another comment)

Not being serious there feller