This talk from the moral psychologist Joshua Greene is a really clear summary of moral dilemmas for laypeople.
Joshua Greene - Edge.org
Greene begins by explaining the tragedy of the commons, a puzzle in game theory that illustrates the intuitive struggle between optimizing one's individual situation vs optimizing the collective's situation. In the tragedy of the commons, the collective is forced to make a sacrifice because of each individual in the collective's rational self-interest.
Our moral intuitions evolved to deal with dilemmas of this sort. People feel an inner urge to cooperate with others despite taking a personal loss. It feels inexcusable to us to walk by a pond while a child drowns, even though rescuing the child would ruin our clothes. Morality is nature's answer to the tragedy of the commons. In each "moral tribe," people learn how to balance their respective interests with the interests of the collective and we all come out the better for it.
But there is more than one kind of moral dilemma. In our modern world, there is increased interaction among people from various moral tribes. We now have to solve moral dilemmas of the kind that evolution hasn't prepared us for, namely that our moral intuitions are useful for maneuvering in our respective environments, but that other groups of people have their own moral intuitions that are good for their environments. There is no universal set of moral intuitions that all groups can agree on. This is what Greene calls the tragedy of common sense morality.
He argues that our moral intuitions simply aren't always reliable. They might be good general guides for getting through our lives, but they aren't the be-all, end-all of morality. Following them on every issue is likely to lead to inconsistency.
A better approach to morality is to have a theory of what makes something good and what makes something bad. Once we have that, we can apply it consistently across all situations. Greene believes that a useful moral theory should focus on the quality of lives: how happy or sad people are. He endorses utilitarianism, the moral theory that asks us to weigh the costs and benefits of our actions to ensure that we are making the world as happy a place as we can.
There are these two different types of thinking: automatic and controlled. These two types of thinking are analogous to the automatic and manual modes of a digital camera. Greene argues that our moral intuitions, that is to say, our automatic mode is good at handling Me vs Us problems. Meanwhile, moral reasoning, i.e. our manual mode, is better for handling Us vs Them problems.