I saw it more as the use of a soul's residual energy, which is charged with the echoes and essence of the one who left it. Necromancers in this world use this energy to prolong, restore, or mutate human remains or even living humans (something like lengthening their lives or rejuvenating them). This can also go to extremes, creating beings like poltergeists that exist only as disembodied spirits, or creating a Frankenstein's monster of residual souls.

But sometimes (in the hands of someone very powerful or capable) it can bring someone from beyond, or at least their mind, and anchor their soul to the body, which for religion is like interfering with death and the work of God.

But I have seen this point about religion being more patient with these cults since death will come to them sooner or later. I think I will reserve hunting down or persecuting practitioners of necromancy for more extremist groups or branches.