Distaste for pain, hunger, curiosity, desire for relations with others, etc. are all present in pretty much all humans. I think there's lots and lots of desires that are universal and the more important the desire the more universal it seems to be.
It is a fair point that people do have some different desires and the relative weights change a bit, and so I think there are some limits here. We get into comparing the utilities of two different people, which is tricky business.
I don't see how dualism is important here. We only need to note the similarity in the brains. I think you're overestimating the variance in the human mind.
CRAP gotta go....... more later.
How do similarities in structure imply similarities in another way?
Well, perhaps this can be analyzed as a logical relation:
'If A then B'. Where A refers to a particular person and O refers to their outcome (E.g in terms of wealth).
From that it does not follow 'If B then O' or 'If C then O'.
I think what we are trying to do in our discussion of equality is establish that every person (A, B and C), implies outcome O. That is, everyone implies the same outcome. So we couldn't justify inequalities.
To do this we must find some sort of identity function such that A=B=C. Thus B implies O. If being is not found in conjunction with O, something somewhere has gone wrong. In a dualistic conception of mind this identity is easy; Given that everyone has the same type of mind there is a very real identity between different people. A genuinely is identical to C.
The problem I see in a materialistic theory of mind is that people are more different than similar, and there is no reason to believe that their similarities should be taken as paramount when determining the relation of implicature between person and outcome.
That is, A and B and C do not equal eachother, they are all genuinely different. And different not just in the minutiae, but the broad strokes.
Thus again, the fact that 'if A then O' does not imply 'if B then O'. When we find inequalities there is no reason to believe something has gone wrong at all. Compared to our original presumption of total equality we are likely to find only marginal equality to be justified.