I agree The Emperor was a major hypocrit , banned Magnus from playing with the warp , what a wolly !
Thats just it though, the Emperor did not ban him from training psykers or using his own powers; he merely banned sorcery due to its link to religion/superstition and lack of training.
Magnus tried to warn the emperor about Horus but he would not listen and did not trust Magnus ,
It was never a matter of trust between the two; the Emperor had told Magnus not to practice sorcery anymore, and his message came years after this. When Magnus sent his message, he revealed to the Emperor that he had not listened and had still practiced.
Its very devestating for a father to learn his own child has lied to him for years about something important. Throughout the entire Heresy, the Emperor shows his own humanity in his unwillingness to see the light of his sons actions; it was no different with Magnus. (But then again, in the end everything that had happened was a plot of Tzeentch.)
I look back at the original post and can only think, the Emperor was not a hypocrit. He banned the likes of sorcery and untrained psykers; sanctioning the training of psykers and librarians as he recognized them as the next step in humanity. Magnus gathered psykers and practiced with them without training, had them practice powerful spells, and had his legion deal in lies and deceit. (Two of the things the great crusade stood against.)