What good is a conscience?

What if everybody stole from everybody. I'm not talking about good and bad now. I talking about daily chaos. If no one could trust anyone else it would be impossible to get anything done. For people to live together there must be trust. Your way of doing things only works if there are always people who do not steal and those who chose to do what's right for everybody instead of filling their personal needs. So, you can never be the rule only the exception. A society of people who only care about themselves would self-destruct eventually. For the betterment of the group you should not steal because you are helped by the group in one way or another.