The benefit of morality comes from the fact that brains are slow to come up with new ideas but quick to recall stored generalizations. If you can make useful rules and accurate generalizations by taking your time and considering possible hypotheticals ahead of time, then your behavior when you don't have time to be thoughtful will be based on what you want it to be based on, instead of television and things you've seen other monkeys doing.

Objective morality is a trick that people who come up with moralities that rely on co-operation play on people who can't be bothered to come up with their own codes. If I learned, suddenly and definitively, that nothing is moral and nothing is right, I wouldn't change anything except to be more secretive about my own morality in order to keep everyone else from finding out that they don't need to follow theirs.