Necromancers: While the Undead are at most times unwilling slaves whom need saving, the Necromancers are not only defying Arkay's will, but enslaving the poor souls of the long departed to do their bidding. This cruelty is an affront to the living that my character cannot ignore.
Most Daedra: The princes like Molag Bal, Mehrunes Dagon, Vaermina and the like cause far too much suffering to the mortal world
The Thalmor: My reasons go beyond political motivations. Empires rise and fall, that is inevitable. They have declared war on Talos though, and that blasphemy will not go unatoned
So there you have it, my enemies are based on religious and humane grounds, what are yours?