Someone claimed "There is no special "Marxist" definition of capitalism"
No, there absolutely is a separate definition of capitalism for communists.
"Capitalism is when bad thing", or more accurately, "Capitalism is the capitalist economic system, every system surrounding it, and any negative consequences of those systems"
See, the normal definition is where capital is primarily owned and controlled by the private sector, free competition, and open markets, rather than the government. In it, people are free to sell their labor for wages to whoever they decide to rather than being directed by central planners, and prices are set by markets and negotiation, not by the state. But most people don't see that as a major problem -- When someone hires someone to do their lawn, or buys groceries with money they earned, or when they can save up for something they want, or if they save money and take a risk starting a new business or building a new invention hoping to make it big, that's considered at worst neutral. It's important to understand that pure capitalism really doesn't exist anywhere, so everywhere is a spectrum -- The United States is more capitalist than the Soviet Union was, but is considerably less capitalist than it was in the late 1800s when the state made up a single digit percentage of GDP.
Some examples of things that aren't inherently capitalist which commies like to blame on capitalism:
-State corruption
-Regulatory capture
-Corporate welfare and bailouts
-State-created monopolies
-Inflation caused by central banks
-Police brutality and prison abuse
-War and imperialism
-Human Greed
-Hierarchy
-Scarcity
-Pollution (Ask Kazakhstan how ecologically friendly the Soviet Union was to their region)
-Cronyism
-Bureaucratic alienation
-Consumer stupidity or status competition
-Poor conditions for the common man caused by state policy
-Unequal political power
Most of these things are either inherent to the nature of reality, or human nature, or the product of the state, not inherent to capitalism, not unique to capitalism, or not generated by capitalism alone. Therefore, eliminating capitalism will never fully eliminate these things. Things like human nature or the laws of conservation of mass or energy or finite linear time will always exist driving scarcity. A group of chickens with no concept of trade whatsoever will establish hierarchies and use violence to that end. Most of human history had limited markets and very powerful states that still had greed, pollution, cronyism, and corruption.
In a sense, it's like the counterpoint to the old phrase "Nobody got fired for choosing IBM" -- if back then you stuck your neck out and chose something other than IBM, you'd be blamed for every problem that occurred because you didn't choose IBM, even if those problems weren't unique to the system you chose and perhaps would have existed if you chose IBM anyway. In the same way, under capitalism, every problem ends up blamed on capitalism, even things that would exist under virtually any other system because of human nature and the laws of physics.
That broader definition has two effects. First, it allows problems rooted in scarcity, human nature, state power, political corruption and large-scale organization to be attributed to capitalism merely because they occur within a capitalist society. Second, it allows the abolition of capitalism to be presented as a cure for the entire bundle. If "capitalism" is defined broadly enough to include nearly every harmful feature of modern life, then eliminating it would indeed sound utopian. But eliminating private ownership, open markets and negotiated exchange would not eliminate scarcity, ambition, hierarchy, corruption, coercion or political favoritism. It would merely change the institutions through which those problems appear.
I was thinking about Ivan the Terrible. His reign was not capitalist, but he had entire cities of his own people sacked. Why? Because he was terrified of losing power, or more accurately, of being assassinated by people. Such people won't go away under a socialist government, they'll be given more power under socialism than under a more laisse faire government under capitalism. Nominally communist countries right now conduct purges in power games where individuals or groups of individuals are murdered to help the powerful get more powerful. Having another group of elites in the market players won't change that. Ironically, having competition between the groups of elites may (but also may not -- sometimes the common man is caught in the crossfire, or is divvied up as a resource to be consumed, regardless of who those elites are)
Related to my soon to be published next book, it is a modernist conception that you can describe the entire world through exactly one viewpoint that can place everything into one system. We do need the government, and we do need God, and we do need markets, and we do need families, and we do need communities, and we do need private societies, and probably a lot more things. Only in a world where many things can exist and bump against each other can the individual hope to have some liberty to pursue happiness.