Here's a link to the full article: http://monthlyreview.org/2009/05/01/why-socialism
The thing is, once you learn about the basics that make capitalism what it is, unless it singularly benefits you, and you're of the upbringing/environment/lack the ability to think critically even if the critique impacts you "negatively", how can you support such a force when there is so much injustice in the world because of it?
How can you support government, insurance, banking, and all other practices that reinforce an inherently flawed system that only favor a few, while dominating the majority of people on the planet and all other non human members of the global biotic community? Ask yourself, do you really want to make a difference in the world?
Do you really care about your species and life on this planet? If so, how could you ever support capitalism? Just because "that's the way"? The dismantling of capitalism as it's been known since the industrial revolution is simply at the roots of a majority of humanity's ills. Period.
Combined with socially constricted forms of oppressions-hate-things people choose to abide by whether they're taught it or not, this is what's hold human back from actualized progression, sustainability and well-being.