Utilitarianism as a Basis for Morality

Can't morality be based on utilitarian beliefs (good/evil being based on trying to maximize happiness and minimize suffering for our society).  It seems like everything can be guided by that principle, because we know innately that suffering is bad and happiness is good -- and we don't need God for that.  So if we just make our decisions to maximize happiness for the most # of people and minimize suffering for the most # of people, why would we need to refer to some other source for morality?