[jerf]

If you wish to understand Spock the character, and the Vulcans in general, at least to the extent that a species written by dozens of writers has a philosophy, it's important to understand that they don't follow lower-case "logic", but upper-case "Logic". It is, itself, essentially a religion (or philosophy if you want to be perhaps a bit more kind) that does in fact carry some base assumptions at its core.

In the particular case of Vulcans, you can definitely have huge, raging arguments about what exactly those base assumptions are, again, given that they were written by dozens of writers, many of whom really weren't trying.

Today you can see the real-life equivalent in the Rationalist movement, which while it certainly permits a certain amount of variance in the base assumptions, does tend to come with a basic set of axioms at the bottom as well.

It would go beyond the scope of what fits in an HN message to actually explain those. (Plus I have some serious philosophical criticisms, which would make it even longer, and also means perhaps I'm not the best person to even try.) My point is merely that when discussing this sort of "logic" it is very important to separate strict mathematical "logic" from the vague set of quasi-religion/philosophical "Logics" that do in fact come with enough base presuppositions to make it possible to debate things like whether enlightened self-interest is or is not "better" than, say, some degree of deliberately self-negating altruism. Upper-case Logic and mathematical lower-case logic are two different words. (And Logic is a family, too, not one well-defined thing.)