The Space Wolves have always been that way, though? Look at Prospero, where Russ effectively decided to ignore the Emperor's request to capture Magnus alive and instead decided to kill him (after talking with Horus), as well as commit a genocide against the Thousand Sons. Then, throughout the books, he has consistently defended the decision, even though Magnus was - at that time - a loyalist. Really, all the books are doing is solidifying what they are: Space dicks who never have consequences for their actions. Hell, even when they have consequences, they don't actually lose anything (see their encounter with Jaghatai Khan and Alpha Legion).