Why is soul trapping black souls considered immoral in the elder scrolls?

In TES lore, soul trapping humanoids is related to necromancy and is believed to be immoral. However, soul trapping creatures is perfectly acceptable.

According to Skyrim Wiki, this is because:

The souls of humanoids trapped in these soul gems remain conscious. They are generally regarded as unethical, and their use is prohibited at The College of Winterhold, despite the institution's lenient stance on the practice of Necromancy. Soul Trapping humanoids is considered a crime in many of Skyrim's Holds.

However, I am unable to find any justification for this from in-game sources.

It's not just soul trapping black souls that is considered immoral, but every aspect of necromancy, from the in game book The Black Arts On Trial (You have no idea how many times I typed Dark Arts...).

Necromancy is inherently dangerous. One cannot 'dabble' in it. The simplest spell requires the spilling of blood, and immediately begins to corrupt the caster's soul. This is not conjecture, but simple fact. It is irresponsible of the Guild to teach and thereby encourage a sort of magickal study which has proven itself, time and time again, to bring nothing but terror and misery on the practitioner and world.

As soul trapping black souls falls under necromancy it will also corrupt the caster's soul. It's also counter to the will of Arkay and anyone knows messing with a god is a bad idea.

There are some things related to Necromancy that are acceptable, the conjuration spell such as Guardian Spirit can summon a spirit from the afterworld, but the difference is that the summoning is with consent unlike with necromancy.

The reason why is because when a soul is tapped in a Black Soul gem, the soul is transferred into a state of infinite torment within the Soul Cairn. They can no longer go to any other afterlife, and their souls will eventually be eaten by the Ideal Masters (rulers of the Soul Cairn).

However, other soul gems just absorb the life force of the creature, and after it is used, their soul goes on to whatever creature afterlife they go to.

It's not soul trapping that is immoral, it is using Black Soul Gems.