Nothing is "wrong" with it, but it is not the same level of critique. Many people like war, I just heard an NPR story about a marine whose leg was badly damaged in Iraq and was very gung ho about recuperating and returning to Iraq. A lot of listeners liked that story. There is a lot of support of "our effort in Iraq." Also many people like degrading the environment - they like hunting and fishing for pleasure, they like sprawl, they want to get rid of the swamps or animals they consider pests. What is more, many people like stopping those considered "undesirables" due to some external characteristic such as skin color, from achieving an equal status - something that you may term "oppression."
In short, oppression, war, poverty and environmental degradation are external critiques of capitalism. Their power depends on people accepting value systems that underlie those critiques, which as I just argued is not always the case.
An internal critique showing that capitalism cannot deliver it sown promise (e.g. maximization of utility or benefits) is better because it does not depend on accepting these external values.
Wojtek