Wait, taking their life is ethically fine and doesn't need to be thought about, but trapping their soul is ethically questionable?

Not sure if this is a response to my post, but I'll take a shot at it anyway. There are a number of rational arguments for why defending yourself or even murder is acceptable, but soul trapping is not.
What if, for example, a body is nothing but a meaty soul trap? Clearly superior to a sword or whatever because it's mobile and
you control it, but if this is your interpretation of life on Mundus, then you're doing someone a favor by killing them and freeing their soul. This idea has some similarity to Aldmeri beliefs, though it's not exactly the same.
Also, if the soul is eternal, and the soul is the true essence of a person, then trapping it--possibly for a long time or forever--is much, much worse than robbing somebody of 30 or 40 years of life. There's also the state of the soul that is trapped. To what extent is it aware? If the soul is fully aware, then you're inflicting a potentially long-term or eternal torture on it. Even if the soul is in a sleep or dream-like state, it's IMO a lot more evil to capture, and/or arguably destroy, the essence of a being then it is to destroy the vessel of that essence.
But aside from Merari's and a couple other people's posts--and even in those I didn't see anything definitive--we don't know what a soul really is, or what trapping one means. So it may be an act of extreme evil, or it may be just a minor hiccup or inconvenience.
Also (responding to some other posts), just because the Aedra say one thing is good and another is bad, doesn't necessarily make it so. To borrow some lines:
KA: "The Lady of the Lake, her arm clad in the purest shimmering samite held aloft Excalibur from the bosom of the water, signifying by divine providence that I, Arthur, was to carry Excalibur. THAT is why I am your king. "
D: "Oh, but you can't expect to wield supreme executive power just because some watery tart threw a sword at you. Oh but if I went 'round sayin' I was Emperor, just because some moistened bint lobbed a scimitar at me, they'd put me away. "
In other words, while many on Tamriel would begin and end their concepts of morality on the words of the Aedra, not everybody would accept them as authorities. Others would prefer to develop their own beliefs through reason, such as the entire Dwemer race, for example (and I'm sure a lot of mages and others).