This thread is awesome! Turns out, I'm a philosophy professor, and I use trolley problems in every class I teach. I just taught Bioethics this semester, and I used it to illustrate the 'Doctrine of Double Effect', which is very close to what Alex wrote. Those who endorse it claim that it is worse to intentionally kill for the sake of promoting some foreseeable good than it is to intentionally promote some good, while foreseeing that a death will result. This sort of reasoning is used to explain why a physician is allowed to administer morphine to a dying patient for the sake of relieving pain, while foreseeing that it will hasten death, but not allowed to administer morphine to kill the patient, for the sake of relieving pain. It also is used in just war theory to explain why 'strategic bombing' is allowed to defeat an enemy, sometimes even when children are collateral damage, but bombing the same number of children, say, in a school, for the sake of defeating an enemy (by demoralizing them) is not allowed.
See, I tell my students every day: philosophy is fun!
