Board Thread:Warhammer 40k General Discussion/@comment-37.152.33.225-20131108174133/@comment-78.51.128.86-20141001204353

To quote the cabal on the dark angels   " legion" pg.166 "there is too much inherent corruption in them."

as to yiur question: fallen angel sheds another perspective on that. there is also a later story that gives more information in the primarchs anthology ...