Greed is typically considered a major source of evil that is the root cause for stealing, hoarding, plundering, and treason, just to name a few sins. However, greed can be good, while other types of greed can be very bad.
For instance, greed is good, because it is the most important incentive for people to work hard, get a good education, start a business, or invest in a company. This makes people productive and contributing members of society. And in return, people are paid a salary, become more educated, and (hopefully) build wealth so that they can in return live a prosperous, more comfortable, and full life.
A second form of greed is for people to continue collecting wealth even after they have far surpassed the amount of money that they need for the rest of their lives. Some people leave so much inheritance that even their children and grandchildren can not possibly use all of it. This is why some people, such as Bill Gates, his wife (Melinda Gates), and Warren Buffet are donating most of their huge fortunes to charity. They understand the virtue of generosity, instead of succumbing to greed. I can only hope that I am capable of such charity.
Third and finally, greed sometimes drives people to do unethical, immoral, and illegal things in the pursuit of more money.
Greed is typically considered the accumulation of wealth for personal satisfaction. It has no useful purpose except to become rich and to continue getting more wealthy. It is a strong desire in each and every one of us that is extremely difficult to overcome. Only through continuously contributing and donating to society can we find true rewards that are far greater than the illusion that greed provides.