This question has been of great interest to researchers. There are a couple of hypothetical scenarios that are commonly used to test the role of emotion in ethical situations:
The Trolley Problem:
There is a runaway trolley barrelling down the railway tracks. Ahead, on the tracks, there are five people tied up and unable to move. The trolley is headed straight for them. You are standing some distance off in the train yard, next to a lever. If you pull this lever, the trolley will switch to a different set of tracks. Unfortunately, you notice that there is one person on the side track. You have two options: (1) Do nothing, and the trolley kills the five people on the main track. (2) Pull the lever, diverting the trolley onto the side track where it will kill one person. Which is the correct choice?
The Fat Man:
As before, a trolley is hurtling down a track towards five people. You are on a bridge under which it will pass, and you can stop it by dropping a heavy weight in front of it. As it happens, there is a very fat man next to you – your only way to stop the trolley is to push him over the bridge and onto the track, killing him to save five. Should you proceed?
In both cases, one is given the choice of taking an action that will kill one person to save five. If rationality were the prime factor, the choice would be clear. But in fact, as many as 90% of people tested can’t make that choice. The Fat Man scenario gives people the most trouble because the action of actually pushing someone to his death is more personal than the act of turning a switch. Again, rationally there’s no ethical difference in the two scenarios, but emotion makes the difference.
Is that a bad thing? Not necessarily. Psychological studies of people who take the “rational” course in these tests reveal that they tend toward psychopathy.