The issue with this argument is that it presupposes a very specific consequentialist framework, where different actions are ranked better or worse depending on one big "badness score" and you pick the one that comes out best. I don't think any virtue ethicist or deontologist would support that way of looking at things. For most non-consequentialists, there are certain features of an act that automatically render it impermissible - not just because that feature jacks up the act's "badness score" beyond anything else, but because it essentially takes the act out of the "badness score" running in the first place. It's just not something you're allowed to consider doing. So if you think using someone's body as a means to an end is one of those sorts of things, then the calculus you're trying to do here isn't even going to get off the ground.
Specifically with regards to the trolley, pulling the switch in the classic scenario isn't using someone's body as a means to an end - it's just acting to avoid harming others in a way that has a foreseeable but unintended harm to someone else. This is also true of pulling the lever in the scenario where the fat man gets crushed. Pushing the fat man, on the other hand, *does* use their body as a means to an end. That is obviously a morally relevant distinction. You're right that the additional suffering generated is important, but it's not immediately obvious to me that, if you're justified in causing someone a certain amount of pain in order to achieve a certain end, you're automatically justified in doing anything to achieve that end that causes a lesser amount of suffering to them.
Imagine a boss who has a legitimate need to make sure his employees are vaccinated from some serious disease. He might fine or otherwise punish a hesitant worker in order to achieve that goal, or he might just inject them with the vaccine while they're sleeping. The former strategy hurts the worker more than the latter strategy, but it seems obvious to me that the latter strategy is still impermissible while the former isn't. So it can't *automatically* be the case that, just because you're allowed to harm someone seriously in pursuit of some end, you're also allowed to harm them in any less serious way. You'd have to do more to actually justify that. "Whatever morality is, it mustn’t be harming the victims of your actions" is too simplistic.
Finally, I'd just say that my moral intuitions are immediately opposite yours in the last scenario. It *does* seem much worse to me to kill someone (against their will) and harvest their organs in order to aid the movement of some other endangered group, as opposed to pulling the switch and having the trolley hit them. Of course, if they were to volunteer their own life, then it would be better to painlessly kill them. But if they don't want to die, then it seems obviously worse to actively violate that wish by direct killing than it would be to cause their death as a mere foreseen consequence of a life-saving act. I think a lot of utilitarians need to remember that their moral intuitions around this stuff are actually somewhat uncommon, or at least not universal, and that merely referencing those intuitions as though they're obviously correct won't have a lot of traction with people.
The issue with this argument is that it presupposes a very specific consequentialist framework, where different actions are ranked better or worse depending on one big "badness score" and you pick the one that comes out best. I don't think any virtue ethicist or deontologist would support that way of looking at things. For most non-consequentialists, there are certain features of an act that automatically render it impermissible - not just because that feature jacks up the act's "badness score" beyond anything else, but because it essentially takes the act out of the "badness score" running in the first place. It's just not something you're allowed to consider doing. So if you think using someone's body as a means to an end is one of those sorts of things, then the calculus you're trying to do here isn't even going to get off the ground.
Specifically with regards to the trolley, pulling the switch in the classic scenario isn't using someone's body as a means to an end - it's just acting to avoid harming others in a way that has a foreseeable but unintended harm to someone else. This is also true of pulling the lever in the scenario where the fat man gets crushed. Pushing the fat man, on the other hand, *does* use their body as a means to an end. That is obviously a morally relevant distinction. You're right that the additional suffering generated is important, but it's not immediately obvious to me that, if you're justified in causing someone a certain amount of pain in order to achieve a certain end, you're automatically justified in doing anything to achieve that end that causes a lesser amount of suffering to them.
Imagine a boss who has a legitimate need to make sure his employees are vaccinated from some serious disease. He might fine or otherwise punish a hesitant worker in order to achieve that goal, or he might just inject them with the vaccine while they're sleeping. The former strategy hurts the worker more than the latter strategy, but it seems obvious to me that the latter strategy is still impermissible while the former isn't. So it can't *automatically* be the case that, just because you're allowed to harm someone seriously in pursuit of some end, you're also allowed to harm them in any less serious way. You'd have to do more to actually justify that. "Whatever morality is, it mustn’t be harming the victims of your actions" is too simplistic.
Finally, I'd just say that my moral intuitions are immediately opposite yours in the last scenario. It *does* seem much worse to me to kill someone (against their will) and harvest their organs in order to aid the movement of some other endangered group, as opposed to pulling the switch and having the trolley hit them. Of course, if they were to volunteer their own life, then it would be better to painlessly kill them. But if they don't want to die, then it seems obviously worse to actively violate that wish by direct killing than it would be to cause their death as a mere foreseen consequence of a life-saving act. I think a lot of utilitarians need to remember that their moral intuitions around this stuff are actually somewhat uncommon, or at least not universal, and that merely referencing those intuitions as though they're obviously correct won't have a lot of traction with people.