I've played Elder Scrolls since Morrowind and still don't understand why they've never really been fully explained on why they're so evil. Until the recent videos of the creators explaining why they want to reclaim Cyrodil, I think it is too late to say that they're really doing it for a good cause. Anybody else agree that they've been seen as evil for too long? I mean I love the Aldmeri Dominion and will participate in joining them when the ESO is released as a Wood Elf Archer.
The Aldmeri Dominion aren't evil. Firstly, because morality is entirely relative in TES: the khajiit people have regarded the Dominion as saviors once or twice throughout history.
Secondly, and more importantly (as it motivates the 4th Era Thalmor), they do not subscribe to the view that the physical world, Mundus, is fundamentally good. http://www.imperial-library.info/content/monomyth-altmeri-heart-world describes the god Lorkhan tricking the deities into creating Nirn, which is a trap, and thereafter they and all mortals (who are descended from divine sources) are bound to reality, unable to escape. Humans (with the possible exception of the Redguard) are Lorkhanic, meaning they are aligned with the forces that the Altmer see as the root of all suffering in the universe. The Altmer oppose men as they are a corruption of the divine ancestors of the Altmer, and the 4th Era Thalmor go as far as http://www.imperial-library.info/content/dominion-prism-textract.