Religion in general, and Christianity in particular, should not be reduced to a question of utilitarianism. There is a moral law in this universe, as sure as their are physical laws that govern it's operation. In each case there are consequences to our actions. If we step off a bridge, we will plumet to our deaths. If we have an affair, there will be repurcussions in all of our relationships.
When discussing religion, ask yourself the following questions:
1. Where do we come from?
2. What has gone wrong with the world?
3. What can be done to fix it?
4. Why are we here?
Christianity answers these questions.