Greed should be distinguished from self-interest. Greed is not good. Greed is grasping for more than you deserve. Self-interest is simply the reality of humanity. By this I mean that each of us cares more about ourselves, our loved ones, and our friends, than we care about strangers. Asking if this reality is good is like asking if gravity is good. It just is.
One virtue of a private-property free market is that it channels our self-interests so that we serve our self-interests best by serving the self-interests of others. I can get a beer from you, a brewer, only by giving you something that you value more than the beer in return. We both gain.
Government, in contrast, unleashes greed. By enabling the politically powerful to grab more than they can get through voluntary exchange, government encourages people with political power and influence to act on their greed – to grab more than they deserve.