>>54442963
Well not 'just' killing things, but war, fighting, murder holds a certain sway over the eldar mind. It is after all what they were made to, and the old ones were nice enough to have them appriciate their purpose.
Its a rush, its a fantastic high and as stated they 'very' easily get obsessed with it.
The dark eldar are just stuck in a cycle, some Deldar act violently and psychotic becasue they are eldar, they affect others who in turn become equally violent and psychotic and in turn they 'infect' others with the behavior. The end result is Commoragh, and the exact same thing could happen on any craftworld, which is why they are so carefull and, dare I say, obsessive in their vigilance.
Its just like the pre-fall hedonism cults, except there is sort of a purpose behind it (refilling their souls).