Actually CSM and Dark eldar are biologically different. They are extremely mutated by the powers of chaos.
Erm, no. Dark Eldar serve Chaos extremely indirectly. They're biologically different from breeding out active psykers and cloning. Not Chaos.
This is like being upset about people differentiating North and South Korea. Sorry, but North Korea, I mean the Imperium, isn't the only side that matters.
oooh I thought some smart ass was going to try that. Not all CSM are corrupted by the powers of chaos. The night lords for example, are perfectly clean. Which makes them the worst of the traitors because while all the others are betraying the Emprah because their minds are being corrupted, the Night Lords are doing it because they are dicks. It's more of a allegiance thing there. Actual corruption is not necessary, but it's really common Dark Eldar, despite what so many think, are actually chaos free. They actually HATE chaos just like all the other Eldar. Again, just like the Night Lords, being evil for the lols. View: https://www.youtube.com/watch?v=x7zEBAo7iDM