Why isn't greed used for good?

You know, philanthropic goals being fulfilled by short term greed leading to the long term benefit of humanity.  Bill Gates founding a college or McDonald's donating to charity are small examples of this, but more obvious ones would be greed through harnessing cleaner fuel sources, or feeding third world countries, providing shelter, etc.  Companies still make money, but get to benefit humanity as a whole.  Or is this too Green Party thinking?

But without giving corporations free reign to destroy the world.