Board Thread:Lore Discussion/@comment-13417807-20130726023954/@comment-24.185.108.132-20150201190753

Well, considering the Thalmor want to:

1. Destroy the last Towers that stabilize Mundus, effectively unraveling creation and breaking linear time

2. "Remove Talos from the Mythic" by stamping out his worship, also working to hasten the end of the world considering Talos is holding back the Kalpic Cycle and also acting as a Tower unto himself by further stabilizing Mundus

3. Not only destroy Mankind, but remove the very idea of Man from existence (not sure how they'll do that, but they want to) so that they can never be rendered mortal again

It's not difficult to see why people dislike the Altmer out of universe. In universe, they (well, their government at least, which represents a majority of them) are fascists that are obsessed with the notion of their racial supremacy and the inferiority of all others, and who have through war, assassination, and violent oppression effectively committed atrocities against every race including themselves. Not nice people no matter which way you look at it.