I think this is a subtle reference (or perhaps not) to the HI Virus.

While they all succumb to the virus, from the drinking of contaminated blood (the whole drinking Sang's blood from a chalice to become a BA), albeit it a psi-/psychoactive type reaction than a physical type reaction.

So everyone is affected by the BAV (Blood Angels Virus), but not everyone will succumb to the crippling Black Rage, but with increasing exposure to The Red Thirst will they hasten the effects.

The Black Rage can also be attributed to the effects of Rabies has on an animal. They get batshit insane and if left untreated, they soon die. They are few examples that people have succumbed to the diseased but have "willed" themselves back to treatment.