I want to add the following, which I believe is rather important:

Question 2: What is wrong with (capitalistic) social safety nets?

The most pressing challenge with these are inequality. As soon as you start charging people for healthcare and social services (like homes for old people), you define that the rich deserves better services than the poor. Why is a rich person more worth than a poor person?

Question 4: If wealth is redistributed somewhat equally, what is the incentive for people to achieve or produce more than they are allowed to keep?

If we define a person's goal in life to be happy, we are getting close to the point here. Because what makes people happy, what is their 'reward' for doing anything good for the community?

The materialistic-capitalistic idea is that material wealth is what makes people happy - and only that. The question assumes the same - if people don't get money and more food, why bother to work more?

People would like to work because of the feeling of doing something for others, because of the friendship you make with your colleagues, and because they want to learn and improve themselves. Quite simply. Very much has been achieved without big rewards or wages.

Update September 1st, 2002:
To add to my last paragraph: E2 in itself is a prime example of this. The reward for spending your time contributing to E2 is merely symbolic (the XP system) and most people do it just to be a nice person in the E2 society.