Marx wasn't even the proponent of a "system". And he was very critical in fact of utopian socialists, as well as people who called themselves "Marxists". The one thing he did was analyzing the exploitative character of Capitalism, nothing more, nothing less. He thought there would be a gigantic uprising of the workers worldwide, but that didn't really happen. Instead the cult of personality under Stalin and Lenin took over in Russia. And they were far from socialist too. Socialism can be summed up in a single sentence; ownership of the means of production by the workers. If there's a reference to private property in socialist literature, it is exactly that; the stuff that Capitalists own to create profit. It is not a reference to personal property, which is your stuff.
Karl Marx wasn't even outright critical of Capitalism, in fact he praised some of the aspects it generated, but only up until a certain point. Beyond a certain point there was just this system that was expanding for the sake of it, serving those who owned the means of production, at the expense of the working class. Today it is also obvious that this goes for the natural environment as well.
It seems to me that this almost phobic cynicism towards Socialism is a very American phenomenon, and I can't really blame them after many decades of fear mongering of so-called Socialism. And of course in the present day, when you have a lot of outrage news that equates Socialists with weirdos, SJWs, etc. There were people in America, in the past who rose up against Capitalists, the robber barons; and these people were no different than the Socialists that were in England, France, or Germany at the time. But dissatisfaction was dealt with by the rise of the...police force. Many people died, not only under terrible working conditions, women as well as children, but also the people who rebelled against it.
Nowadays we live somewhat comfortable at the expense of the third-world, as well as China. Just check out the conditions these people live under, and then tell me that this Capitalistic, neoliberal system is in any way in favor of human prosperity, both material and non-material. But America, from what I have seen and read, is also in a terrible state; the great rise in homelessness, gentrification, the epidemic abuse of substances, the elderly, poor and disabled that get screwed over, the rise in suicides and violence towards others, the decline of a feeling of community, the overall hopelessness of the average person who tries to hold his head above the water in this neoliberal nightmare.
People who may not be in favor of this system have to live under it, and cannot currently escape it. They have to make use of certain means to spread awareness of the problems it creates. If you were a peasant in feudal times didn't mean you had to like living under these conditions. There are plenty of films, music, literature, and indeed even video games that expose the system we live under. Take the cyberpunk genre for example. How many times do we complain, on this very forum, about the exploitation of the consumer per week? Well, that is because of this very system that is in place people. We all complain, but not everybody is willing to put their finger on the problem. Even Oddworld's creator, Lorne Lanning, said that Capitalism has been detrimental to gaming. Why? Because it needs growth, just like a cancer.
I don't even consider myself a socialist or communist. In fact, I'm leaning towards Anarchism. But I have to give credit to Karl Marx, as he was right about a lot of things, for instance that economic upheavals are endemic in a Capitalist society.