HTMC said:
You have a weird definition of evil :-P
It comes from when I was studying philosophy back at the university and I was faced with an ages-old philosophical conundrum: What diferentiates a brutal prince from an evil prince? Quite a tricky question, because the brutal prince will perform acts that can be viewed as evil, and the evil prince can be brutal in its cruelty.
After much pondering, the answer I gave on my essay is that the difference boils down to motivation. A brutal prince does evil, yes, but it does so not out of malice but as a means to an end. Perhaps he finds it most expedient, perhaps he believes he would appear weak otherwise, perhaps he believes he's being tough but fair. Regardless, he doesn't necessarily enjoy it and his actions still are, at least from his perspective, done for the good of his people. The evil prince, on the other hand, enjoys his brutality, does evil acts because they amuse him and if they're beneficial for his people, it is coincidental, not his motivation. He only thinks and acts for himself with little to no regard to the damage he may cause or the consequences of his actions to anyone other than himself.
Another component of my definition is another philosophical conundrum of whether you can truly call virtuous someone who has never been tempted. I expand on that claiming that you cannot say something is evil when it is incapable of choosing to do good.
Thus by my metric, the Dark Eldar are evil to the extreme. Others combine different levels of evil and brutality, but for the Dark Eldar it's as if their evil had been processed through an alambic to produce 100% pure, high-octane evil distillate. They have no motivation other than hedonistic, cathartic self-gratification. They had the capacity of choice and are fully aware of the pain and damage they're causing. Indeed they do their evil precisely because it's painful. Their evil has no grand purpose, no ulterior objective, it isn't the means to and end, It just is.
Evil for evil's sake.