Freedom of experimentation, i am free to find solutions to problems and nothing is taboo when it comes to solving problems.
You are anything but free, traitor. You are forever shackled to the service of your heretical gods. You are nothing but pets being rewarded for appeasing your masters.
We are all slaves to our limits, our failures. It is a matter what we do with our time that determines the value of our lives.
You have to understand, we left the imperium due to being shackled to the skeleton guy on a golden throne. We get treats and we get rewarded, ever considered you get nothing, they take you ,modified you into a superhuman D.N.A enhanced super guy, then you lose your memories and then you serve in ignorance of who you are or where you are from and you die like a slave to a guy who is LONG dead but still claims 1000 lives per day. Tzeentch the chaos god promotes free experimentation and those who are willing to break that which is taboo to reach the goals one is after, even assists in his own ways.' Nurgle saved an entire legion the death guard from dying of an plague, and trust me if it was up to the imperium they would have all been burned to the ground. Khorne grants warriors his blessings if you serve him well and fight in the battles. And Slaanesh who is a muse and likes music, art, beauty and lust you follow that which makes you happy. We may be puppets in some regards but trust me it is far better being puppets and enjoying the life of chaos then it is being part of the so called "imperium of man" which is pretty much worshipping a skeleton on a throne. And lastly....."For the emperor" is he not your master which you try to appease and who rewards you nothing in return? Take a good look at the rotting edifice that is known as the imperium, and think again, what are you actually fighting for? for who? and do you truly have free will?
I just can't imagine fighting for some moldy corpse but the play style of marines looks fun so I go for a more evil path and go with chaos. Also I agree with Spirit of Rock (at start of thread) with the whole rigid moral compass thing and playing Chaos allows me to indulge myself in the cruelty I see others enjoy.
For the legion! Grandfather Nurgle saved our legion. Now that I am the very thing that once sought to end me, death, I serve the Nurgle and our Lord Mortarion as they see fit.