there is a huge global problem with concentration of wealth, and with the way that access to wealth is unavailable to massive swathes of the world's population. there are many that believe it is unjust to celebrate the individual freedom of rich people to get richer when there are hundreds of millions that are basically starving. this argument is very old, but also very real. and because of how that wealth is concentrated, it is difficult to make a clean and cogent criticism of it without looking like you are railing against something ethereal or spectre-like.
the fact that a system was established that brought prosperity is not a relevant argument as to whether it could (or should) be better, or whether there should be something esle instead. in many parts of the world, this question really is about the right to earn money, the right to eat and the right to have an opinion.
i think people that are taking part in this want a system with less emphasis on wealth generation and more on justice. they want a world (and a leadership) that is willing to stand up for a different set of priorities that focus on increasing standards of living and decreasing overall suffering rather than standing up for the rights of single individuals to get the most wealth possible.
the american system was set up on a basic principle of individual liberty. that sounds ideal, but the reality of it is that it creates intense competition from a playing field that was never level. this has led to an ever-concentrated centre of wealth, and a huge amount of 'injustice'. and the amazing thing about it is that people have been hoodwinked to think that any disagreement with that is a threat to freedom.