So, we are on a fictional planet where the most powerful human faction (the Union) relies heavily on necrotechny (high-tech necromancy) for historical reasons. Necrotechny brings prosperity and military power to the Union as detailed in the examples below.
As the Union progressively became a democratic federation with a focus on human rights, so the practice of necrotechny became open to debate. Foreign countries are mostly hostile toward the black arts and their ideas permeates the society.
What could be the arguments in favor of maintaining the practice of necrotechny?
I guess one of the first thing they could try would be to attach it to some tradition, but I am seeking some way to justify necrotechny on an ethical ground.
Examples of potentially problematic necrotechny uses by the Union
The Deathguard - an ever-growing regiment supplied by the unclaimed bodies recovered throughout the Union. These soulless undead soldiers keep a limited intelligence (enough to use weapons efficiently but not to drive vehicles) and are remotely controlled by military necrotechnicians. They are used as cannon fodder or in risky environments. About 5 millions deathguards (20 times more than the human military personnel) are stored in necropoles.
Forensic necromancy - after a violent death, occurring while the body was not weakened by ageing or disease, souls roam on the place for a few days. Police investigators can use it to solve murders, but the capture and interrogation process damages the soul (i.e., loss of identity and memory).
The Ascended - an assembly of prominent characters that were granted extended life for their deeds in living. They are partly sentient undeads who keep their human likeness thanks to embalming techniques and regular maintenance. Creating an Ascended is a costly process performed only twice or thrice a year. They are more kept as living memories than actually implied in society. Their will gradually fades away and they 'die' a few centuries after their creation. About a thousand exist at the time of the story.
Reanimates - assemblages of non-human bones and artificial parts, imbued with the soul of an animal used as automates in factories. They can feel some degree of pain. Their use is almost universal across the Union.
Additional details regarding the world
The technological level is mostly similar to the Cold War era, with the notable omnipresence of magitechs. Globalisation occurred a century ago, some sort of magical AIs/internet exists, primitive spaceships carry satellites to low orbit, mass destruction weapons deter aggression against the major factions, and human activities threaten the ecosystem.
In this world, the existence of souls for living beings is scientifically proven. Souls do not create new memories but can still answer questions regarding their past and feel basic emotions. If not captured, the souls are slowly drawn toward the center of the planet where their fate is unknown.
Powering of the undead require a small quantity of ichor, a liquid extracted from underground deposits (~ magic petroleum). Ichor is the prime resource for powering anything in this world and the undead is especially cheap.
The undead are restricted to do what the necrotechnician set them to do in the resurrection process, so an undead uprising is very unlikely. If released from this control, the undead construct simply dies.
The other human factions rarely use necrotechny. Outside of the Union, necrotechny is seen at best as unsettling. Extremist religious groups consider it as a monstrosity. The Union itself is mostly atheistic.
EDIT - Necrotechny cannot cure diseases as it operates exclusively on dead bodies. Using it as a way to prolong one's life is described as the Ascended case above.
EDIT - Some concerns voiced by the citizen opposed to the practice of necrotechny
These techniques promote the exploitation and commoditization of the human body.
Necromancy harms the Soul.
Necrotechny disrupts the normal cycle of life and death.
Note - I am not a native English speaker so it may happen that I use some words outside of their standard definition.