Saying communism would work if people weren't so greedy is like saying painting everything the color of baby shit would work if everyone were blind or that a boat with a hole in it would work if water was thicker. Develop a system that compliments human nature or you didn't really develop a system.
Actually, there're enough decent people in the world to make communism work, but shame they're not hypocritical enough to make it to a political seat.
The only political system that works is the one that exists as a conference and all power vanishes after the conference is over. Limit 30 days a year. The power goes back to the people to exercise the laws and means themselves.