> That's not the question. I'm not asking why humans tend to do something.
I suspect that you are ... or you are indeed asking a nonsense question. But let's see ...
> I'm asking why should one person's suffering or one person's life be intrinsically important to another---not why it often is.
OK. I'm still not sure what exactly you mean by that question, though.
> To get to the point another way. To decide how to act you need some kind of ethical system.
Sure, that seems sensible to me.
> Let's say you pick utilitarianism.
OK.
> Utilitarianism says that the suffering and happiness of each individual counts equally.
I am not sure it necessarily does, but I guess that doesn't matter for the point that you are trying to make, so let's assume it does ...
> The obvious question is: "Why is that so?"
Which is a "how" question in disguise, isn't it? "How did it come that philosophers chose to define utilitarianism this way?" That certainly sounds like a very much empirical question to me!?
> A possible answer is that, this is the premise that leads to the optimal outcome of maximum total happiness.
That might well be a justification given by some philosopher, sure!?
> Which leads to the next question: "Why is maximum total happiness the optimal outcome?"
Which is another "how" question in disguise, isn't it? It's again asking for how it came to be that this was considered the optimal outcome, isn't it?
> It's never ending. There is always another why question. Going deeper and deeper into that rabbit hole can be maddening and it's not always useful, but sometime it is. Ands it's almost always useful to ask a few whys.
Well, if they are "how" questions in disguise, yeah, sure ... but you might as well directly ask the "how" questions in order to avoid the confusion? If you really don't mean a "how" question by those (be it exactly the ones I suggested above, or possibly slightly different ones), though, I don't really understand what your question is here either.
> Without asking the whys, you have no justification for any of your beliefs, and thus no way of knowing which beliefs to hold on to.
Well, yes, again, if you actually mean disguised "how" questions. I mean, just asking the question doesn't give you a justification, right? Rather, it's the first step towards potentially finding an answer, which then can serve as a justification. It's just that "why" questions that are not "how" questions in disguise don't have answers, which is why they are useless for the purpose, or if they have "answers", then that's only because the answer is assumed in the question, which obviously doesn't make for a good justification for anything.
I am still curious though what exactly it is that you mean by "I'm asking why should one person's suffering or one person's life be intrinsically important to another"!