[NiteRabbit]

The problem is, Abaddon is seen by the majority of the Black Legion as the successor to Horus' legacy and if he chooses to disassociate the Legion with Horus, then that's his decision to make. Abaddon essentially rules with an iron fist so that even if someone did want to question him they would be crushed or forced to leave. It is not unreasonable to think that perhaps a Chaos Champion would still want to preserve the legacy of Horus but they would no longer be allowed to call themselves a member of the Black Legion if they did so. They'd probably break off and form their own warband, although, having said that, the people most likely to have attachments to Horus' legacy are the original Black Legionnares, the ones who were part of the Sons of Horus from the beginning, and the only one we know the fate of at the moment is Abaddon himself. Any others would likely have agreed with him or have been crushed already. The newer Black Legionnares would probably not feel the same connection to Horus that the original ones did, making it easier for the Legion as a whole to disassociate themselves from Horus.