@ Angelus Censura
The Angel sanguine are the only BA succesor chapter known to never remove their helmet (or at least hide their face), and Red Fury makes it seem like they are the only ones. (Main character wondering why, Flesh tearers mocking them about removing the helmets)
"However, why would only a select group be affected while others are fine?"
Actually I would think that only a chapter(s) would be affected, as they may have done something / played with / treated the blood or gene transfer differently. Or something completely different? I am not led to believe this would be translated easily to your AI theory.
I'm not sure about the whole AI thing as this thread is the first I've heard of it, I have however heard a lot about the Vampire theory, I just figured all Blood Angels would be affected vs just a sucessor Chapter. But it didn't occur to me that each successor Chapter recruits in their own way and would in turn handle the implantation of the gene seed differently. As cool as the AI is, if all we have to go off of is a Lexicanum article stating "will of iron", I highly doubt that is enough evidence to support some sort of neurological implantation. It could simply be just a metaphor or choice of words from the author.So my guess lies with the Vampire theory. Which, if following old legends, Vampires cannot handle sunlight, which could translate over to them not removing their masks to avoid the light. Also, if their fangs have become grotesquely long, their skin pale, and eyes black, that would make sense as well - if they were to be seen without helmets like that, the Inquisition would shit their pants