Thank you for providing this information, digging to everything on there on my own would have been a monumental task.
So basically the Space Marines have become heretics and traitors, and not just a few but all of them because of some documents which anyone with even a slight degree of paranoia would probably condemn as forgeries. Especially Space Marines who have been psycho-indoctrinated to be utterly distrustful towards anything with possible xenos origins.
The problem with much of this is that the Space Marines are at least as xenophobic as the majority of the Imperium, this change makes them seem too much like rational do-gooders, which they aren't, they are the super-soldiers of an evil realm. They are not enlightened philosophers, they are the iron fist of the Imperium, tasked with routing out its worst enemies in an uncompromising way, they do not ally themselves with the impure or xenos, they ruthlessly crush all opposition. A space marine is not a policy-maker, he (or rather, it) is a soldier, created to kill and destroy.