The theory goes like this: capitalism combines with consumerism and advertising to make us sad, lonely, and forever chasing after material goods. So we consume endlessly and the Machiavellian capitalists reap the rewards. It's not a great theory.
Competition for wealth and social status was hardly created by the capitalist system. People have always competed for these things. Thanks to capitalism, though, this competition is now less violent, and true poverty is easier to avoid.