From Roger Scruton’s On Human Nature (pgs 95-96):
A spectral version of moral reasoning can survive in the world of the trolley problems; but it exists there detached from its roots in the person-to-person encounter, lending itself to mathematical treatment partly because the deskbound philsopher has thought the normal sourches of moral sentiment away.
That is not to deny that moral reasoning makes comparisons. When Anna Karenina ask herself whether it is right to leave Karenin and to set up house with Vronksy, she is asking herself which of two courses of action would be better. But although she is making a comparative judgment, it is not one that can be resolved by a calculation… Her dilemma is not detachable from its peculiar circumstances … Dilemmas of this kind exist because we are bound to each other by obligations and attachments, and one way of being a bad person is to think they can be resolved by moral arithmetic. Suppose Anna were to reason that it is better to satisfy two healthy young people and frustrate one old one than to satisfy one old person and frustrate two young ones, by a factor of 2.5 to 1: ergo I am leaving. What would we think, then, of her moral seriousness.