Unfortunately, the actual basis for one judging what actions are moral is quite complex. There is no set moral compass.
One might think so - but that is because you are assuming your value set is universal. Or should be. That usually leads to simplistic analyses of what one should do when this debate comes up.
You decide if saving someone is worth your life. Is saving that life worth the disruption to your family? Is feeling sorry for yourself if you don't act, a good enough reason to act?
People make decisions on two levels. Quick and emotional, slower and rational.
If you want to discuss this seriously and without cliches - a good starting read is:
The Social Psychology of Prosocial Behavior by John F. Dovidio, Jane Allyn Piliavin, David A. Schroeder and Louis A. Penner (Apr 25, 2006)
If you say that you don't need to study up because you know what is moral and right and wrong from your gut - you make my point about simplistic views.