It's not at all greed. Any Money fills 3 functions:

1) Unit of account
2) Store of value
3) Medium of exchange

Money simply means that I can sell my old camera then maybe buy some pizza with some of the proceeds vs trying to find someone will accept a camera for a pizza, and then give me something that is worth the camera-the pizza for change. Money fulfills a function that allows an economy to work to some degree of efficiency.