If one wants necromancy to be inherently evil it is good idea to add some sort of metaphysical drawback like suggested here in some posts. Zombies being somewhat dangerous if the operator screws up really doesn't rise to the level of inherent evil to me.
Reposted from earlier-
Okay, let's see. Here's 10 (I only needed 10) quotes from the PHB. Read them together and see what you think.
1. School of Necromancy (PHB 118)
"Most people see necromancers as menacing, or even villainous, due to the close association with death.
Not all necromancers are evil, but the forces they manipulate
are considered taboo by many societies."
2. School of Magic (PHB 203)
"Creating the undead through the use of necromancy spells such as
animate dead is not a good act, and
only evil casters use such spells frequently."
3. Animate Dead Spell (PHB 212-13)
"Your spell imbues the target with a
foul mimicry of life, raising it as an undead creature. ... The creature is under your control for 24 hours, after which it stops obeying any command you’ve given it."
(note that if you are creating zombies and skeletons, you are
creating evil creatures where there were none ... you are not summoning or binding already existing critters)
4. Druids (PHB 65)
"Druids accept that which is cruel in nature,
and they hate that which is unnatural, including aberrations (such as beholders and mind flayers)
and undead (such as zombies and vampires)."
5. Paladins (PHB 82, 84, 86)
"Even so, their martial skills are secondary to the magical power they wield: power to heal the sick and injured,
to smite the wicked and the undead ...
The presence of strong evil registers on your senses like a noxious odor, and powerful good rings like heavenly music in your ears. As an action, you can open your awareness to detect such forces. Until the end of your next turn,
you know the location of any celestial, fiend, or
undead ... As an action, you present your holy symbol and speak a prayer censuring fiends
and undead ..."
6. Detect Evil and Good (PHB 231)
"For the duration, you know if there is an aberration, celestial, elemental, fey, fiend, or
undead within 30 feet of you ..."
7. Hallow (PHB 249)
"Everlasting Rest. Dead bodies interred in the area
can’t be turned into undead."
8. Raise Dead (PHB 270)
"
The spell can’t return an undead creature to life."
9. Resurrection (PHB 272)
"You touch a dead creature that has been dead for no more than a century, that didn’t die of old age,
and that isn’t undead."
10. Negative Plane (PHB 300)
"Like a dome above the other planes, the Positive Plane is the source of radiant energy and the raw life force that suffuses all living beings, from the puny to the sublime.
Its dark reflection is the Negative Plane, the source of necrotic energy that destroys the living and animates the undead."
So, does a necromancer absolutely have to be evil? No. It's says so. But ... repeatedly animating the dead is evil, because:
A. It's taboo in most societies; and
B. It violated the bodily autonomy of the individual (in a world where there is certainly an afterlife); and
C. It prevents the person from being raised; and
D. It creates an evil being where none existed before; and
E. It uses the energy of the Negative Material Plane, which is NOT GOOD BOB; and
F. Read in its entirety (including the existence of spells to prevent people from coming in and raising the dead) it's clear that the base rules strongly mean that animating the dead ... aka, creating evil creatures to serve your bidding and keeping those people from ever having the chance to live again, not to mention not getting their consent, is an evil act.
You are welcome to modify your campaign world so that this isn't the case, and you're welcome to ignore ideas like what constitutes "good" or "evil" (or even having those ideas), but that's the base rules.