Why is creating undead Evil?

[Troacctid]

[citation needed]

No, seriously - quotes, please.
Because I read it, but don't seen where it was "covered"
So, may you highlight it or something?..

Here's a few. There are more.

That sounds like an argument people would make in-universe. The obvious counterargument is that all uses of negative energy don't need to be evil for animating the dead to be evil. Mabaran power can be channeled safely, and animate dead is unsafe. Like driving a car without an exhaust filter.

It's true that negative energy itself isn't evil - but neither is radioactive waste, and pouring it into a lake or meadow would still be an evil act.

Per Libris Mortis, negative energy makes it easier for uncontrolled undead to enter the world that the necromancer didn't intend. There are a vast quantity of undead creatures that can arise spontaneously from various circumstances, and LM/BoVD state that unchecked necromancy can mean more of them. Nobody knows exactly what makes some executed serial killers become Mohrgs while the others simply die off for example, but in nations where necromancy is widespread, you will get more of the former. Similarly, not all neglected children become Slaymates and not everyone who dies with unfinished business becomes a Ghost, but the ones that do likely do so due to some presence of "ambient" negative energy.

The spell has the evil descriptor, which has clearly defined mechanical effects. The undead it creates also have an evil alignment, which has mechanical effects as well. Seems like the mechanics are all neatly locked up. The more interesting question is, what kind of story do we want to tell? Why does it matter to the plot?

The [evil] descriptor is enough evidence that it is, therefore the burden of proof that it isn't is actually on you.