It's about being able to "channel" the magic in the blade and evoke the power of the enchantment. In case you didn't know, those "Reduce Spell Cost by X%" enchantments function by improving your understanding and ability to handle the magic. A novice of Destruction is wasteful, spending a lot of energy/soul power in a weapon to evoke the effect. A master of Destruction (Whether that mastery is from training or Enchantments) can evoke the full force of the magic by drawing upon just a tiny charge. The reason someone with 100% Reduction in Magic keeps the soul there is because he's not spending it.

Activating a magic item is kinda like using steam to spin a turbine - A novice wastes a lot of that steam in a large, unguided discharge that causes the fanblade to spin slowly because it's undirected. An adept can control the stream, greatly reducing the amount of steam needed to send that turbine spinning rapidly. Someone with 100% Reduction in Magicka Cost is essentially building a pipe around the turbine, not letting any of the steam escape.

For a mage, the source of the steam is their magic pool. For an enchanted item, the source of the steam is the soul. A skilled enchanter can make a more efficient reservoir to hold that mystical steam-anologue, but it still comes down to the user to guide and direct the steam to spin the turbine. Or, to end the metaphor, the end-user uses his own magical skill (Not reserves) to draw upon the magical reserve held within the item (The soul) and engage the power of the item. Enchanted items are no longer "Idiot-proof" like they were in past games.

TL;DR - You're erroneous in your assumption that Magicka-cost-reducing enchantments affect the user's magicka - They actually affect the user's efficiency in directing the energies of that school.

Like someone mentioned above we steal the souls of immortal beings on a daily basis, why do you care about the morality of stealing mortal soul? In Skyrim YOU are the biggest freakin soul gem in the world!!! You are a dova who kills other dova just to prolong the inevitable end of this kalpa. The dragons are only doing their jobs and you are stopping them from completing their duty and stealing their very life and knowledge of their own existence! (Then the crazy man took a chill pill and fell asleep.)

But for a dragon, absorbing it's soul is merely a momentary time-out.

For a mortal, it's agony, especially if the soul remains in the item for a great chunk of their once-lives (Such as being used to initially charge a weapon, remaining chained until the weapon's destroyed).

Good point. I didn't think of it that way, props to you.

Source? I haven't read anything that says what it's like for the devoured dragon soul. I was under the impression that devouring meant devouring in the sense that the dragon soul's identity is dissolved permanently and its power incorporated into the dovahkiin's own soul. So Alduin was only resurrecting those who had not been slain by a dragonborn or another dragon.

When you absorb the soul of a dragon you also absorb its knowledge ( according to the grey beards).

That's the closest thing I have to an answer. So yeah..

I'm curious about the dragon souls too. Isn't absorbing their souls a form of soul-trapping?
Is there any official information about what happens to the soul of a dragon once it's absorbed? Or what happens to the soul after the Dovahkiin dies(if he/she ever dies).

I've trapped hundreds of bandit and other rather.. unsavory people's souls in my azura's star, i think they deserve it.

There's really no way of knowing if a dragon has a consciousness anything like a mortal's. There's some reason to believe they may perceive time, the world, and selfhood quite differently. In any case if they don't want their souls eaten they shouldn't spray down towns full of people I'm trying to do quests for with frost breath.

It's not a "Real" Soultap, in the lore you absorb the knowledge, like you just read a book in 0.1 second.

Hehe. Me to. Bye bye thalmor

It's a soul devour. You eat them, quite literally. Lick the flesh right off their bones.

Great, thanks for that mental image.

I have hundreds more where that came from. Just skip a smooth pebble into a fog covered pond late at night, and if it skips back, you may get another.

You can see it in-game.

All those Daedra you promised yourself to apres-vie are gonna' be in quite the shock when the come to claim you, only to find a chiliocosm of roaring dragons telling them in one voice "Back off bub, or we're gonna' have problems".

You're making me google stuff again. I always imagined it as a Highlander type deal where if you kill every single dragon you're promised a prize, but the prize ends up being some intergalactic BS that makes no sense by the time you get to Skyrim 2.

If you truly absrobed all their knowledge you woul just kill an ancient and know all the shouts, and much more about the normal forms of magic as well. Apparently Dragons know a lot more about enchanting. A dragon taught mortals how to bind 2 enchantments into 1 object after all. You have to use 1 eye and 1 hand for each enchantment.

Now I've gone crosseyed!

Is it evil to trap Dogs souls and such in Stones?
Yes

Is it evil to capture Vivec and Ulfric's souls in gems?
Nope

Joking aside, it all depends on your point of view

Heard somewhere that souls trapped within soul gems are in constant agony.

It would depend. Surely the souls of all the Cyrodiil Emperors within the Chim-el adabal aren't in agony. That would be frightful.

And there's that quest in Skyrim where a necromancer intentionally soul traps himself in Azura's Star to live as an immortal in his own pocket-dimension-paradise.

Yes but he slowly went insane. Whether that's to do with the Star or Azura's machinations, we don't know. But it was no paradise.

He was kind of upset about being disturbed though...But it is fairly stupid to try and set up residence in a Daedric Princes favorite artifact and expect nothing to go wrong...