Capitalism assumes that all people are self-interested. Furthermore, it asserts that people should act on that self-interest in order to achieve the greater good. A simple example of how this works goes like this:
Farmer John harvests his field of corn and stores enough for himself and his family. The rest he sells to the grocer in exchange for money that he uses to buy other foods/supplies from the grocer.
A free market exchange of goods has taken place where each individual acted out of his/her own self-interest. The farmer did not sell his corn to the grocer because they were friends, but because he needed the money. The grocer did not by the corn out of pity, but because it was good business and he knew he could sell it for more to his customers. Both acted self-interestedly and both benefitted and probably thanked one another as they left. Thus, out of self-interest, both parties end up helping one another and the greater good is served. So why is this a problem?
First of all, it's void of personal morality. It expects people to act selfishly with no concern for the wellbeing of others. This is contrary to the yes you can concept which expects people to care for one another, to lift up and edify, and encourage greatness. It expects service and virtue while capitalism works on a foundation of selfishness. It gets away with this by claiming that such behavior is actually better for everyone in the long run. While it may work to the benefit of many, it is clearly not beneficial to all in every case. One clear example of this is the way businesses get involved in politics in order to influence policy in a way that creates a market advantage for that business. This is clearly unfair and usually ends up wasting public funds for private purposes. Yet this is exactly how we should expect a pure capitalist to behave. It is in the self-interest of that business and all its shareholders to ignore the greater good of the rest of society and to use public funds and the democratic system to secure their own fortunes.
Many other criticisms of capitalism such as income inequality, commercialism/materialism, exploitation, etc. all have some validity. I believe the root cause of these faults is selfishness. Capitalism is built on the foundation of self-interest. One may argue that not all capitalists are wholly selfish as is shown by large charitable donations and other altruistic acts. However, in such cases, the alleged capitalist is not adhering wholly to the capitalist philosophy. Some other philosophy is in play there. One that expects altruism, morals, and concern for one's neighbor. One that is much more in line with the yes you can concept than a capitalist one.