Why is Necromancy evil but Conjuration is not?

[Max_Killjoy]

So going back to the discussion of alignments being beyond human comprehension, I can see a few takes on it.

First, good means "good as outsiders define it" rather than "good as humans define it" then I would say humans ought not concern themselves with the objective definitions of good and evil and instead view them as they relate to humanity.
It would be no different than humans in the real world trying to take into account the ethical systems of ants and termites; they may exist but they don't relate to humanity.

Second, if good and evil are universal but they don't actually have any detectable consequences, they are just good and evil for their own sakes, then we get back to the gods as Abe Simpson model.

Third, we can have the book of exalted deeds system, where isolated good and evil acts cause suffering in the universe ignoring the normal system of cause and effect. For example, if I animate a zombie, force it to good deeds for twelve hours, and then disintegrate it so it cant harm anyone it may seem good, but then on the other side of the continent a family suddenly comes down with the black plague or a greedy landlord decides to evict an orphanage during a blizzard.

IMO this last is much better suited to an existential horror setting like Call of Cthulhu than a high fantasy game like Dungeons and Dragons.

Two of those produce a setting in which mortals in the setting (and the game playing at the table) should firmly ignore the Alignment system entirely. In the first, a moral system that's incomprehensible even utterly counter-intuitive in some cases, resulting in mortals not being able to discern Good and Evil, is useless, and as you state they should just proceed with trying to do the right thing as best they can... because they have no way of avoiding doing "Evil" by simple innocent accident. In the second... if Good and Evil have no impact, then just go do the right thing and forget Good and Evil.

The last is the sort of cloud-cookoo-land nonsense (the book's claim, not your paragraph) that awaits at the bottom of the rabbit hole of Alignment as Cosmic Forces.