To be fair, the emperor didnt do much to Mortarion. He saved Mortarion's life. He even organized whole Nikaea thing, so Mortarion could be happy. Problem is, Mortarion was very hard on the Tyranny part. He did serve the emperor, but he also hated him for being a tyrant he is...kind of hate and love relationship. The Empy and his second in command being a dirty psykers didnt help also. And, since his relationship with Horus was way better, Mortarion decided to join Horus, when Heresy has began.
As a child of Magnus and seeker of truth, I have come to this conclusion. "Chaos" is a phrase used by the ignorant for what they do not understand. To call it Chaos denies it's reality but not to call it Chaos denies the fact of its being. Ultimately it is a source of energy, knowledge, and power that can be understand just like math. To uneducated, an equation in math is a mass of lines for which they can not determine meaning. Chaos is but the same. Yet! Although I do not believe we be should controlled by Chaos. Too many pay too much for their power, and power means nothing if you sacrifice what you are to get it. I stand to be the master of my own fate, rather then a pawn. You might claim I am arrogant, and there might be truth to this claim. But I claim Tzeentch as my example. He is unchanging in the fact he is always changing. There is never a point he does not change. Reality changes around Tzeentch, Tzeentch does not change around reality. If Tzeentch were to stop, he no longer be Tzeentch. This is way I follow my life, I will change the warp to benefit me and work with gods to benefit me. But I will not change what I fight for or who I am, for to do so I would stop being who I am and be someone else. A pawn. So I might follow Tzeentchs ways, but the ultimate lesson I learn from Tzeentch is one must deny him to truly be a avatar of Tzeentch.
A simple response would be it depends upon which army I am supporting at the time. Overall however, Chaos is a difficult subject given how self-contradictory it is on the whole, and initiating a severe problem when trying to have one viewpoint on the subject. You can find truth in its words, inescapable truth which cannot be denied, but for every one of those you then find two dozen lies or fabrications that same truth has been built upon.
Just a couple of guys, hanging out and playing halo while snorting coke of a daemonette's multiple asses. That is true chaos.
All followers of chaos are the same thing,,, cowards and oath breakers. The forces of chaos, as strong as they are, have been fighting for 10,000 years and still have lost/ abandoned 12 black crusades, Thousands,,, if not millions of conflicts and still they feel so proud of killing humans that cant fight back. So in essence,,, Chaos is a bunch of whimps that cant fight anything more dangerous than a human thats been awake for about 3 days straight and just about to fall asleep, And then brag about that kill as if they just killed the emperor in 1v1. (that is if you read any books conserning loyalists) But my hope is,,,, chaos is not going to win. Once the primarchs that are still alive, Russ, Johnson, Corax, Vulkan and the Khan (Guilliman and Rogal Dorn get a special mention for guilliman being in that stasis field, and Dorn for there only having been found one of his hands) apear again, chaos is going to fall apart. That makes 5 realy pissed of primarchs able to lead the imperium. Then there is the speculations about the Emperors revival... If that happens you have a pissed off Emperor.
cha·os ˈkāˌäs/ noun complete disorder and confusion. Even if chaos wins, in the end, they will start a war between each other as they can not share the glory, power, or control of the universe. They each must have it for themselves.
