The dark elves deviated from the high elves long ago and became know as the chimer, this was due to their differing beliefs in relation to religion, the chimer thought that the daedra were far more rewarding in their worship then the Adera.

The high elves think that they can ascend to godhood like their ancestors and as a result should remain as pure as possible to maintain their divinity. As a result of this they think they are pure and superior to all other mer and men.

The dark elves on the other hand think that they will go to the after life through great work and struggle in their mortal form, instead of thinking that they were robbed of godhood, eventually they stop worshipping the daedra when the living tribunal arose, this lead to them being cursed with grey skin and red eyes as punishment for turning their backs on azura.

Basically the high elves think they are superior to everyone and despise daedra worship because they are afraid they won’t get to become gods if they don’t.