Witches with good bloodlines and excellent talent enjoy preferential mating rights, and generally, no one considers compatibility with lower bloodlines.
Even among the witches, it's like this, so it's easy to imagine how much other races, without unlimited evolution abilities, value bloodlines.
Interestingly, before the emergence of the Witch Clan, the biggest rebels against bloodline theory were actually the vampire clan, although they are also its staunchest supporters.
The rebellion of the vampire clan against bloodline theory lies in their ability to grant other weaker races a chance to reverse their fate.
No matter the race, they can choose to abandon their original race through the ritual of First Embrace and be reborn as vampires.
From then on, they discard their weak original template and embrace the powerful vampire clan template.
But they're called the vampire clan, named for blood, so how could they possibly not care about bloodlines?
