Selfishness ruins everything. You can't mix selfish people with unselfish people and expect to get a well functioning community. Incentives and accountability can help, but I am skeptical about whether the latter alone can ever solve the problem.
IOW, for a community to function well, there must be some way to expel or "kill" people who break the moral rules of the community. The ultimate incentive is that if you don't conform to those norms, you will be eliminated.