Whether God exists or not is irrelevant. Most people cannot be trusted to do good unless they feel like accountability is inevitable. God's omnipotence provides that along with a clear moral path. Also, people have an innate need for God (some could argue this is evidence of existence) which if not nourished will just manifest itself in bizarre and degenerate non-deity based religious movements like the political Left. Last believing in God promotes humility because you are not the rulemaker of your own universe. Basically, believe in God if you can.