So the five people are somehow special because they are more numerous? So special, in fact, that I have a moral obligation to murder a man just to save them?
I don't necessarily agree with him on this, but it definitely isn't as black & white as you would like us to think.
The first thing I would ask is, do things change if it's one life for 10,000? If the answer is yes, then count back to the point where that decision changes and let me know what it is.
The answer isn't simple, but all other things being equal most people agree (literally as this question has been studied) that saving a net 4 lives is the right thing to do.
Its also a choice that could easily be made different depending on, as I said in another post, information.....
Let me tell you what I said the first time I had heard this question posed to me.....
I said all other things being equal, then it made sense to save a net 4 lives......Then I proceeded to ask more about the men and if any other information was known. I was told no there was nothing else I knew about the men.
The problem as I said in another post is one of information.....Because as we know, all other things are rarely equal.
Let's say I had pulled the lever and found out that the 5 men were a work detail from a local prison serving life sentences for murder and the one man was just an employee. A good family man with 5 kids and a wife.
Was what I did immoral? Well in light of new information it's easy to judge what i did in that light, but the morality of my action should be judged in the light of information I had at the time. It is possible for an action taken to be moral, but immoral given better information. Now we can argue the nuances of what I should have known. In other words, judging an im/moral act and the person that did it should judged separately. This is why, I suspect, you are hesitant. Because you know that society will judge your actions in light of information that comes available after the fact, whereas you might be more willing to act if you know society knowingly embraced the idea of information known at the time based on societies dedication to study and understand morality.
Some scenarios that might have change our decision to pull the lever.
What if the 5 were old men and the one was a baby?
What if the 5 were middle aged men and the one was a man who was on the cusp of curing virtually all disease?
What if the 5 were attempting to commit suicide together and the one wanted to live?
What if the one thought the train was coming his way and he wanted to die and the five wanted to live?
The point as I keep reiterating is that morality is a whole lot harder than some rules written down. Most people want their morality served up to them in simple easy to digest morsels so they don't have to think beyond those ideas. Morality to them is 10 rules written in the bible, while others believe that you have to read the bible cover to cover. Others believe that the NAP is a good guide to morality, while you say the NAP is a good start, but you have to define it in context. Judging rules in context just means employing your own intuition. All I'm arguing is, educate your intuition.
Morality is something that we should all dedicate and challenge ourselves to. Morality cannot be derived from a few commandments or a few paragraphs and then forgotten about until it's time to deploy it, because the reality is that for many of the moral decisions we make the guidelines of NAP, utilitarianism, Kant's morality all of them aren't complete. As long as new information is available, morality should evolve based on that information.