In response to Cryhavok:
First and foremost, I'm not trying to offensive in any way, I'm just looking to both express my beliefs and convey my own knowledge on the subject.
I don't mean any offense either, I just like freindly arguments about this subject
No Inquisitor in their right mind would have killed Lorgar at that fist meeting. You're forgetting that the Inquisition sees the Emperor as a religious figure, just like Lorgar. That was Lorgar's biggest failing, he needed something to have faith in. He was reliant upon it. So when the Emperor denied his Godhood and made the entirety of the Word Bearers' Legion kneel by force despite their spreading of His glory, Lorgar was disillusioned and found something new to worship, something that would accept his praise and his efforts. The Chaos Gods. In my opinion the grand majority of this started because the Emporer denied the religion surrounding him that bloomed into being anyways.
And The emperor, who started a crusade to eradicate such unfounded religions amongst other reasons, who is one of the most powerful psykers ever, did not forsee this betrayal? Lorgar started as a "Heretic" from the religion of Reason, and defied the emperor with his every breath. He was not capable of bending his thoughts around a concept to make it into what he needed. Had he pursued reason with religious zeal, he probably would have been fine.
As for the conclusion that no Primarch should have been Warmaster, that's just kinda silly. The Emperor expected proffesional, concerted military efforts as opposed to the unease and squabbling that pervaded the crusading legions. He made the slight mistake of forgetting that as Superhuman as his sons were, they were nonetheless his sons. Picking one out of all the others to make the decisions smacks of favoritism to a son, where to a militaristic mind it's a decision that had to be made. Even King Arthur and his Knights of the Round Table, who sat in a circle with no one at the head of the table in an effort to symbolize equality, King Arthur was the inevitable decider. All militaristic organizations need a head.
The Emperor's work back on Terra was FAR too important to be left alone. It was worth leaving the Crusade for in the first place, his brainchild and his own little pet project Manifest Destiny for humanity, and he just up and left. It was huge. Read Thousand Sons and you'll get some idea of the scope. I give no spoilers.
I will admit, I have not read that book. My premise about no primarch being the warmaster was not intended to make the assumption that the emperor stay and lead. More along the lines of someone like Malcador, who was in his own right immensly powerful be put in charge.
Also, every single one of the Primarchs had their crucible of sorts. Mortarion led a revolt his pseudo-father who was the tyrannical warlord of a toxic planet. Lorgar lead a holy war against those that didn't believe in his visions of the Emperor's coming. Curze was Batman, and eliminated ALL crime from his PLANET. Leman Russ grew up as a viking, and the Crimson King mastered every psychic power available to him on prospero and started creating more, he became a planetary leader with all of the responsibilities that that entails.
Yes those were crusibles… on our scale. However each of the primachs was capable of tearing a human warrior apart with his own hands without any difficulty AS A CHILD. By the time these genetically-engineered-warriors-designed-to-conquor-the-universe primarchs were full grown adults, I don't think there was anything left but another primarch to provide a suitable crusible with which to challenge them. Thier behavior and attitudes in the books I have read (my opinion) supports this by making them seem like spoiled children rather often, whenever they are faced with a TRUE crucible. My opinion was that the first TRUE crucible any primarch faced was by Lorgar, losing his religion to the emporer's command, and he failed it. The second was horus when he was struck down… and he failed it. One of the things that I noted to myself when I read several of the books was that all the primarchs had certain individual traits, but they were magnified to huge proportions and where those traits were concerned they had little control over themselves, something they share with children everywhere.
Also, as to Magnus' fall. Magnus did undoubtedly go against the Emperor's word, but let's be fair about this. The World Eaters have their berserk fury, the Word Bearers have their faith. The Emperor's Children have their quest for perfection and the Space Wolves have their controlled ferocity. Without their Psychic fury, what sets the Thousand Sons apart aside from the ravages of mutation set upon them? Should they have lost their psyker abilities they may still have been Astartes with all that that entails but they would have been robbed of their niche. As juvenile as that sounds, it's pretty important. They would lose their purpose. And so they rebelled. But that's still not why Magnus fell. Remember that thing I mentioned earlier, about how the Emperor left the Crusade for the sake of working on a more important project, something more important than the expansion of humanity? Yeah, Magnus royally ****** that up. Then during the burning of Prospero he sat in his tower mumbling to himself while the Vlka Fenryka ravaged Tizca. Eventually he couldn't take the deaths of his sons any longer and so he fled to the warp. He tried to take the judgement upon himself but he couldn't bear to watch his sons die. That's a paternal instinct that I don't think could've been avoided. Should the Emperor have brought Magnus into this project of his from the beginning, everything of the sort could have been avoided. (I am a huge Magnus the Red fan.)
Never read that book so my perspective does not include that. My assertion is from the idea that psykers and sorcery are seperate things (ala dark heresy) The emperor did not forbid psykers, infact his other legions even had librarians at that time (if I remember correctly). Magnus was forbidden from sorcery, and had he followed this edict the psykic might of his legion would have remained immensely impressive. His defiance of that is what cost him. If your take on the universe does not differentiate psyker from sorcery then I agree my assertion would be wrong. He also failed his TRUE crucible. That being said, my first model was a thousand sons sorceror, they have always been my favorite, although I like Ahriman more than Magnus.
As for him choosing to subject humanity to the ravages of the Xenos filth and the Daemonic scum….I have to think you're dead wrong. At the point he's at, where he can control the entirety of Terra with no issues unlike any empire could have ever done or kept up and he's done it for hundreds of years. You just impose the same policies on a galactic scale. It makes no sense for him to turn brother on brother in an effort to stabilize anything. There's Xenos and expansion for that. To split your forces down the middle is a detrimental move no matter how you spin it.
I will admit this is purely based on what I feel like believing the emporer was like and is not based on anything in the lore at all . I think NONE of the major powers are anything but evil in 40k and you will only find good people and heros at the individual levels. So Following that I think the emperor was pretty freaking evil, that he did nothing out of benevolence, and that mankind is still following his plan for human ascension… and that in the end he will win. I also believe that the emperor is a pantheon on his own and is equal to the pantheon of the four chaos gods, but individually each chaos god is not a match for him. But again, nothing in the lore proves either way on this (as his true motivations could never be known today) and this is based on my own fancy.
As for the primarchs turning theory of mine, the idea was that it was intended far down the road… after the galaxy had been clensed of all that xenos filth and other threats. Not every plan works exactly as intended though, and the emperor fell prey to this. The Chaos Gods, knowing that this was set up to happen took advantage of the opening lorgar gave them and engineered this to happen before time. Again, just my own fanciful musings though, not based on anything in the lore.