When I first looked into 40k, or more specifically the Horus Heresy, I thought CSM's were "forced" in a way to turn to Chaos after one or more of them became "tainted". Having to do more with some crazy Jedi mind tricks and not like a rebellious teenager trying to give his parents the finger. I'm still not sure which one it is... Maybe both?
why people worship chaos? because when all Space marines were loyal and everyone followed the EMPRAH the imperium pwned the galaxy so something opposite had to be created in order to spice things up. also so we can have this scene: View: https://www.youtube.com/watch?v=XRTPYYMyoSU
I'll give you one word, no wait make that two words: Horus heresy Of course if you disagree with that, there is: 1.) the age of apostasy 2.) the Nova Terra Interregnum 3.) Moirae Schism 4.) First war for Armageddon 5.) Months of shame 6.) Battle of Prospero (This one is my most favorite reason) 7.) Destruction/poor care of the squat race 8.) Anything that makes the Emperor look like a god 9.) Matt Ward 10.) Inquisition and Grey Knights 11.) use your Imagination Okay that covers it, if you still don't believe me then you truly are a loyal, crazed, fanatical follower of the emperor and shall die a painful death at the hands of either chaos, dark eldar, orks, craftworld Eldar, Tau, Tyranids (nom nom nom!), more insane emperor followers (No one expects the Inquistion!), or Necrons. Have Fun!
Papa Nurgle is the nicest guy, especially when you are corrupted past feeling pain. Nurgelites are actually very kind to "family" and cannon friendly.
Erobar, I've fought countless times, yet I've never met an adversary who could offer me what we Salamanders call "A Beautiful Death." I can only hope, that with all the universe gathered against us, there might be one who's up to the task.