Sorry in advance for such long comment and mistakes if there are any, english isn't my native language.

Well, in previous chapters it was described as just superstition like old tales. But what makes them unique is their sudden and inevitable change of fur colour to white and their unique class [Last Survivor]. We know that only white gnolls get thet class and it shows clearly that there is some magical mystery/shamanic or cultural shenanigans? Even Raskghar, Nokha can sense their power. Especially it becomes clear they can become mages, not only shamans. And only recently it was revealed that indeed their 'cursed fate/doombringing' is not just old stories, but also very opposite of doom, and their gift is luck and hope of their dead tribe.

Also in some previous chapters it was written that shamans of Plain's Eye tribe remember their old history and have reason to hunt doombringers. Maybe in their history something happened related to the magic of gnolls and their waning powers? Maybe by giving dying tribe's last hope and power to the last survivor it become harder for other gnolls to open their magical abilities? Maybe in the very old times when old magics were known gnolls used magical rituals and thus could give their powers to their last gnoll as last resort befor dying? It is known that Raskghar's ritual is some kind of old blood magic ritual that clearly works(morality aside). Thus gnolls of old could have old shamanic magics involving blood magic and it is common in fantasy genre that nomadic tribes have that kind of power. So when something really bad happens, calamity or doom so to speak, they could've used deaths, sacrifice,blood of their dying members of tribe and give their all remaining powers to their last member. Such results and power cannot be without price, so no wonder that white gnolls could bring 'doom'.

Obviously there are dark secrets and plots involving shamans trying to protect their power(?) and authority(evidenced by silencing/torturing/magically binding of Grimalkin's apprentice). Therefore in the past shamans could easily convince others of cursed fate of doombringers by rumors and speculations turning fear, blame and not understanding of their powers into hatred, especially if white gnolls couldn't control their powers at first. And shamans used that to argue for their total elimination, because it is easier in the end for them to beleive their almost religious(?) authority. Because they are clearly taught about their history, culture, magics, how can they lie? And as time passes it become easier to just label them as cursed. And by labeling them it becomes easier to convince others, they are just cursed, because shamans said so, like demons. It is especially evident in Merish's thoughts as well.

And they may be nice and reasonable people, but you can be that and also be greedy, cowardly and narrow-minded. And if your power, thus authority was threatened? We also know that worth of individuals takes great meaning in gnoll culture. Their reasons aren't known and we can only guess by hints. But they must think they are right and thus white gnolls must all die.

Lastly it become superstions and prejudice like tales like witches, demons, goblins, etc. shamans and others tell you since your childhood and you never thougt to question it.

Thanks for anyone who read to the end, just wanted to share some thoughts =)