Sonja's ability to get away with murdering so many Pretenders with no retaliation makes perfect sense as Evil Is One Big, Happy Family absolutely is not in play. All of them see each other as potential rivals or slaves so they don't care when others of their kind are killed.
Sonja's rapid breakup with Palmer and his seeming indifference to her after Lethe's absence makes perfect sense due to Sonja applying Laser-Guided Amnesia to their raising of Lethe. So much of their relationship was based around their shared status as parents that he probably barely remembers any of their good times together.
The entire world is positively drenched with supernatural monsters that not only feed on blood and flesh but also human misery. Humanity is also so jaded and uninterested in looking for the truth that only sensitives can see them...and they're dismissed as mad.
Almost every sensitive who finds out about the supernatural world either goes insane, is committed, or decides to serve the Pretenders.
