Out of sheer curiosity, how come Eldar and Dark Eldar have so bad standing? They're usually each others' most trusted allies (not trusted, mind you. They don't tend to trust anyone)... There are nearly none recorded large scale conflicts between them and several cases of mutual aid. It's not high and dark elf situation of 'worst enemies and total opposites'.
Their ways are different, but both see each other as only civilized people in the universe...
They're battle brothers in 40k chart for a reason...