How come the Chapter secludes Psychers, but not Null-Psychers?
In the past, the Emperor of Mankind forbade the Adeptus Astartes to have Psychers within their Army. – Many Legions went against this command, including the Primarch; Magnus the Red, that was eventually destroyed on order of the Emperor. The Emperor was immersed within the Golden Throne before being able to revoke all Astartes Psychers however, and this has lead to that most Chapters did, and still do go against the Emperors orders regarding Psychers. – The Guardian Angels however remember the Emperors orders, and refrain from including Librarians in the ranks of their order. Still, the Chapter needs protection from Psychers, and ways to train against them or test new initiates for psychic potential. To do this, the Chapter keep “the Brothers of Silence”. – The Null-Psychers that nullify psychic abilities and reveal psychers through the sheer terror of life drain. – The Emperor never gave a order against Psychic Nulls, so the Chapter is well within their bounds using such individuals a
