Let's tone down the personal insults, eh?
You ARE manipulating magical properties in the ingredients to make potions. The praxis of alchemy was laid down by Galerion like all the other magic skills. http://www.imperial-library.info/content/fundaments-alchemy which I linked to up above describes using the magical properties of the ingredients:
"Often overlooked by aspiring mages, Alchemy is a time-honored, rewarding discipline that can change the lives of those who master it... Many items in our world, mostly organic in nature, can be broken down into more fundamental essences with magickal properties." Alchemy is the process of taking natural matter and purifying its magical essence. It requires magical skill (not necessarily spellcasting) to do this.
From http://www.imperial-library.info/content/feyfolken-i:
"Magic as we know it today comes from Vanus Galerion. He restructured the schools to be understandable by the masses. He invented the tools of alchemy and enchanting so everyone could concoct whatever they wanted, whatever their skills and purse would allow them to, without fears of magical backfire."
So, if you care about such things, your warrior can't use alchemy and stay "pure." Whatever in Oblivion that means.