Magnus shed what remaind of his loyalty to the imperium of man and to the Emperor when he refused to be killed by Russ, up till then all his actions were still (Ar least in his mind) geared towards the salvation of the imperium, as soon as he used the knowledge/power Tzeentch gave him to teleport himself and his entire legion of Prospero he officially became a plaything of Tzeentch (Arguably he always was).
The planet of Scorcerers was created by tzeentch to mock magnus and his legion as much as it was for them to use it as their home-base.
If he didnt join Tzeentch he had 2 options watch the remainder of his legion devolve into monsters, or die as he was meant to at the hands of Russ.
Magnus made the choice for the legion, the rest had no say in it, he may have been smart, his legion may have been preeminent in its understanding, but lets face it, in hindsight they out of all the legions were down right retarded, Magnus always believed he could control the warp, always felt he was more knowledgeable than the emperor, he didnt listen in Nikea, he didnt listen to his adopted farther, he didnt listen to his brothers, he always thought he had the answers, vanity and pride was his undoing and by extension his legions.
Ahriman embodies these values, he believed himself above Magnus, blinded by his own perceived superiority, he against the Emperors decree and that of magnus went ahead and did his Rubric.
What they both have in common is they both think they are the masters of their fate, yet at every turn they are guided, mislead and ruined, Ahriman thinks that he dosent serve Tzeentch yet every act he has perpetrated since the Heresy has done nought but empower the changer of ways.
(Anyway we still need at least one more novel of the thousand sons to really know what happened on the planet of the sorcerers and magnus's motives).
Magnus destroyed more than Horus and Lorgar did together, they may have brought the galaxy to the brink, but he imprisoned the Emperor, destroyed the Imperium's future and nearly destroyed Terra.
Last edited by Lost&Damned; 08-04-12 at 04:38 PM.