This is an issue I deal with in detail in my Principles of Economics classes. The fascinating point about the market system isn't that it is based on greed, but rather that it forces those motivated by greed to act in ways that promote the social interest. If you want to get rich, say by x amount, then you better improve the lives of consumers, through voluntary transactions, by some amount greater than x.

Such are the economic means of acquiring wealth, explained in more detail in 1922 by the German sociologist Franz Oppenheimer, writing at a time before his discipline transmogrified into an enterprise predicated on supporting greater state intervention.

However, problems arise when those motivated by greed find ways to acquire wealth through coercion. Oppenheimer called these the political means (as opposed to the voluntary means of the marketplace), and we witness them today when (1) firms benefit from their relationships to the state as opposed to the consumer, and (2) the state itself uses its legal monopoly on violence to acquire wealth.