Why is everyone in this general obsessed with Eldar / Dark Eldar? Can't think of anything more boring than "elves in space".

I'm relatively new to the lore / world of 40k. After reading a good deal, is it just me or is chaos the good side? Seems like heretics and servants of chaos are at least doing it under the pretext of helping the laypeople of the imperium. Kind of a class struggle, whereas those who support the GEOMK are just trying to maintain the class structure status quo, where they benefit from mass exploitation of the masses.

Not saying chaos itself is good, but the intentions of those who follow it are admirable.