Board Thread:Warhammer 40k General Discussion/@comment-2253300-20130211000751/@comment-7671639-20130415041241

Also space marines minds are wiped not only because to keep the Grey Knights secret, but because usually the space marines have seen demonic horrors that would haunt them in their dreams for enternity if they did not.(Think about how many good space marines went insane when they stormed Horus's Battle Barge right before the final battle between the Emperor and Horus.)