[nonameiguess]

There are metasocial reasons for this that are probably best illustrated by one of the classic variants on the trolley problem. Imagine you're a surgeon in a hospital. You have a healthy patient who is under for knee surgery or something. At the same time, five people come into the trauma ward from a trolley accident down the street, all of whom will die without an organ transplant. All of them are compatible with your patient.

What should you do? If you're going to take the view that failing to save a person you could have saved is morally equivalent to killing, then clearly you should kill your one patient to save the other five.

But think of the longer-scale effect this would have. Would anybody ever go to a hospital and get elective surgery knowing they might be killed to harvest their organs? A more general form of trolley problem doesn't necessarily present that exact dilemma with such clear consequences, but at any scale, think of the consequences of being concerned with what happens because of your inaction. Do you donate blood once a week or whatever the max frequency is at which your body can regenerate the red cells? Do you still have both kidneys? Do you ever spend money on anything except bare minimum shelter, enough grain to stay alive, and every other cent going to the AMF or whatever the maximum QALYs saved/dollar donated charity is? How many people have died in your time on Earth that could have lived if you'd done something different? If we all seriously made that a primary concern in our daily decision-making, virtually all productive action would be paralyzed. Everybody would be trying to become a hedge fund manager living like a pauper and giving all their money to the AMF, but the AMF would no longer be able to do anything, because everyone would be a hedge fund manager and there would be no one left to manufacture mosquito nets.