That's a pretty absurd thing to say. There's lots of theory that isn't descriptive of capitalism like Kapital is. Pretty much all of Lenin's main works except Imperialism deal with how socialist society should organize.

"What is to be done" VI Lenin.

First of all, we have plenty of real world examples of socialist societies, and plenty of Marxist theory has been written by people living within these societies. Second, we don't need a blueprint for a perfect society. The goal is to recognize the problems that we have, try come up with solutions, and iterate on that. It's the direction of travel that matters.

yes you have to understand the actual thing you are fighting against. plenty of theory (and practice we can study!) dealing with how to defeat capitalism.

Did those who advocate for abolition of slavery have intensely detailed plans for how an economy would function post-slavery, complete with successful examples of societies that built some other economic system after slavery?

Marx and Engels spoke just enough about future socialism to provide the framework. They didn’t fill in the details because that is not possible, there is no one-size-fits all blue print for socialism. Each time and place has its own specific context that must be accounted for. Ignore that and you will likely fail.

Also, Marx and Engels whole point was to describe the history of all hitherto society, and how class struggle defines that history. To try and authoritatively say “this is the precise next step” would be undialectical and anathema to their entire approach.

Just because Marx's most important work is Capital doesn't mean he, Engels, Lenin, and countless others haven't also written about how to bring about socialism, and how that might be achieved. We even have real, existing socialist societies like Cuba, the PRC, and former USSR where brave revolutionaries have helped show us the way forward.

Yeah Karl Mark's really very much described capitalism but if you're not reading the other Marxist writers you're doing yourself a disservice.

Lenin in particular is incredibly important to understanding modern day communism. Mao includes blueprints for the successful Revolution that he threw. Even if you don't like Stalin or appreciate his actions in the USSR he wrote a ton on communist Theory and given that he led one of the most powerful countries at one point seems like it might be prudent to you know hear what he has to say.

And that's not getting into people like Rosa Luxembourg. Oh Hoxha has a ton of writings which get up to the '90s. Michael Paranti has also added a lot.

From the economics point of view there's people like Richard wolf who's a marxian economist who brings a marxian element to Modern economic theory.

You're incredibly naive if you don't think people haven't thought about how to fix the broken system that we've been living in for the better part of a couple hundred years now. It's out there you just have to go find it and not fall for the United States or Western lines "on what doesn't work"

People have and still are building socialism, and there are many existing socialist states. Many westerners just dismiss them out of hand, either because they're chauvinists, and/or because they believe every negative thing capitalist media tells them about existing socialism (which validates their supremacist outlook).

That's an interesting but unrelated idea given that all currently existing socialist countries only became socialist because of revolutions that had popular support from all sectors of society except the owners of capital.

that's why we need to abolish private property in the means of productions

Which is why capitalist shitholes of the west are now visibly coming apart at the seams.

so i take it you haven't read theory

Agreed, capitalism being forced upon us all is doomed to fail, comrade

Socialism has overall largely come into existence in places where it's popular among the people, as it's a proletarian-driven system. The opposite is true of capitalism.