Emp's Ruling on Psychers

"Hear now the words of my ruling.
I am not blind to the needs of the Imperium, but nor am I blind to the realities of the hearts of men. I hear men speak of knowledge and power as though they are abstract concepts to be employed as simply as a sword or gun. They are not. Power is a living force, and the danger with power is obsession. A man who attains a measure of power will find it comes to dominate his life until all he can think of is the acquisition of more. Nearly all men can stand adversity, but few can stand the ultimate test of character, that of wielding power without succumbing to its darker temptations.
Peering into the darkness to gain knowledge of the Warp is fraught with peril, for it is an inconstant place of shifting reality, capricious lies and untruths. The seeker after truth must have a care he is not deceived, for false knowledge is far more dangerous than ignorance. All men wish to possess knowledge, but few are willing to pay the price. Always men will seek to take the short cut, the quick route to power, and it is a man’s own mind, not his enemy or foe, that will lure him to evil ways. True knowledge is gained only after the acquisition of wisdom. Without wisdom, a powerful person does not become more powerful, he becomes reckless. His power will turn on him and eventually destroy all he has built.
I have walked paths no man can know and faced the unnameable creatures of the Warp. I understand all too well the secrets and dangers that lurk in its hidden darkness. Such things are not for lesser minds to know; no matter how powerful or knowledgeable they believe themselves to be. The secrets I have shared serve as warnings, not enticements to explore further. Only death and damnation await those who pry too deeply into secrets not meant for mortals.
I see now I have allowed my sons to delve too profoundly into matters I should never have permitted them to know even existed. Let it be known that no one shall suffer censure, for this conclave is to serve Unity, not discord. But no more shall the threat of sorcery be allowed to taint the warriors of the Astartes. Henceforth, it is my will that no Legion will maintain a Librarius department. All its warriors and instructors must be returned to the battle companies and never again employ any psychic powers.
Woe betide he who ignores my warning or breaks faith with me. He shall be my enemy, and I will visit such destruction upon him and all his followers that, until the end of all things, he shall rue the day he turned from my light."