The Aeldar (along with the predecessor to the orks, the krorks) were created by the Old Ones to fight the necrontyr/necrons and the C’tan during the War in Heaven.

Also whether or not characters or legions deviate from the Imperium’s ideology is unimportant as they are still supporters of a theocratic, xenophobic, authoritarian, ultra-militaristic, and ultimately fascist regime. This sort of argument that the Space Marines and such aren’t fascists because they split away from the broader Imperium ideology is like when Nazis try to argue that the Wehrmacht were made up of average soldiers so not all of them were Nazis. Its irrelevant, they are still fighting to support a fascist regime which makes them a fascist. The only times Space Marines have ever actually split enough from the imperium to reliquish their loyalty to it is when they end up swapping to Chaos (which is just as bad, if not worse). My favorite faction, the Red Corsairs, being a perfect example of this.

Also the Orks are a charicature and parody of british hooligan culture.