Quote Originally Posted by InvisibleBison View Post
Objections to creating undead tend to come in four general categories, not all of which may apply in a given setting:

1) Creating an undead from a body harms the body's soul in some way.

2) Necromancers are incentivized to kill people in order to have bodies to use.

3) Undead, when not properly controlled by a necromancer, will attack the living.

4) Undead are gross.

In the scenario you're describing, 1 is not the case. 2 can be avoided by using trustworthy necromancers and/or keeping a close eye on the necromancers. 4 is not such an issue in a desperate situation. The only problem I see is 3 - what happens if the necromancer is killed or loses control of her zombies? Of course, that's less of a moral issue and more of a practical one.
There is also (5) - the act of necromancy, even when it doesn't do one of the first four things, metaphysically harms the environment or otherwise hurts innocents in some indirect way. This is the one various editions of D&D have gone with, and more importantly is much harder for an aspiring necromancer to offset or mitigate than the others.