Unfortunately, Real Capitalism has never been tried before...
The point is to show the contradictions of market liberalism, how they never fulfill their ideals and by necessity lead to the conditions under which we live. Communism simply says: let's live in a society without money, without a state, without class. Where one fishes in the morning, hunts in the afternoon, and debates in the evening. Where we live, produce, and labor in a social fashion, where people's basic sexual and physical needs are always attended to as the highest priority of the collective. Where each and every person is given the opportunity to pursue the fullest extent of what they can be as a person, to flourish as a human being.
Somewhere in here the Soviet Union fits in: for having the highest degree of sexual freedom, for guaranteed housing and jobs, for fair working hours and a living wage, for gender parity in all aspects of life. All at the expense of a vast police and security complex employed to crush potential dissent, and to use those political prisoners as a free pool of labor in order to compete with western late-capitalist states (which they failed to do).
The Dengists succeeded by simulating market capitalism to generate the industrial conditions necessary to move towards a more fully socialized state--the Soviet Union, on the other hand, was never willing to subject their backwards populations to industrial capitalism, which led to even greater violence in some respects. People wonder how far it will actually take them, we'll see...but the CCP seems to be uninterested in an internationalist movement.
I think that the basic propositions of Communism are mostly appealing, its just that people are not sure how to get there. We've had successes, like the Paris Commune, that were ruthlessly crushed by the state--they don't tend to last very long. Is there a way to achieve revolution without strict military disciplinary measures? After all, the hierarchies of an army nearly reproduce the hierarchies of capitalism with marked precision. Short answer, nobody knows, the French almost had a successful revolution in 1968, that failed, they spent many decades theorizing why, alternatives to an armed movement. Foucault, the great French theorist against disciplinarian social organization, became a neoliberal. Many of those who descend from these french thinkers became Neoliberals, like Jonah Peretti (who founded Buzzfeed) or Nick Land. You could also call them accelerationists, who believe that by accelerating the contradictions of capital one can bring down capitalist society faster, as it will end up crushing itself.
Everybody knows the system doesn't work, we're all sick of it, but nobody knows what to do about it. Everything else besides plain and simple labor organizing seems like a lost cause. Anybody who says anything else is usually confused or in someone else's pocket. We had a nearly international, decentralized protest movement only a few years ago that could've toppled multiple governments if the people were angry enough. You don't think the people won't get angry again?