The system works on a small scale where each individual is a cherished member of the group. People look out for the wellbeing of each person.

A family unit is a group like this. You don't pay your mum to make you dinner. She makes it out of the goodness of her heart.

Some villages worked like this - until barter systems came along.

It's not just about greed though. It's about fairness. If I'm working all day to provide for everyone, but there are people that sit and do nothing all day, why should they reap the rewards of my work? Communism is a noble idea, but it works only if everyone works for a common goal.