I think its pretty evil to trap a soul who wants to go to an afterlife in your weapon and exhausting it in combat
Well in TES souls don't go to the afterlife. They just reincarnate into new people.
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To answer the poll.
1. No. It's evil to bind a persons soul in a black soul gem. I won't even try to defend that.
2. Is it OK to trap an animals soul? I'm a bit on the fence with this. I don't think its right. But I'd do it anyway if I'm attacked by one. I won't actively go looking for animal souls to bind.
3. Is OK to trap a spirit's soul? This is one more complicated. I would have zero problem with trapping a lich's soul, or an evil spirits. But a zombie? I would be apprehensive about because not only were they resurrected without choice, their soul has to be confined to slavery as well. Though even as I say this I would probably bind a Zombie's soul as well.
4. Is it OK to trap a summoned creatures soul? I don't think I would. I mean its just rude. The creature is already bound to help you. I feel its just adding insult to injury to soul bind them as well. I won't do it.