Finally! You get it just like me! The red dragon doesn't care about humanity, he despise them, hate them but not as to kill them all. It's just that he cannot feel empathy for them. He will kill them for a reason. The royal family because they started the massacre, the hero (knight) because he wanted to see him in despair while her impotent daughther watched, the innocent queens to give out a message, he doesn't kill aimlessly, but looks like that, like a psycho, since he doesn't care about humanity and doesn't care about small details or prudence in front of others. He doesn't want to have empathy for those who murdered his kind. But Zek, he actually is doing his own agenda, patiently killing the ones who killed all the dragons. It's just that he's taking his time. I came to like the story after putting my shoes on the red dragon and is quite nice
Also i think the white dragon is unable to understand him since Mc (Wd) always lived alone. So she didn't meet other dragons or have anyone to talk to, so she doesn't have prejudice or kindship. That's why you all feel her nice and like her, because she's oblivious to reality and doesn't dare to harm humans now. So yeah, she's nice to all of you, and for the red dragon she's just like him, and that's what makes him feel like he's not alone anymore. It's not love or pederasty, he's grabbing the last string of sanity he has on her as hope. Like if you where in a world full of murderers of humans, and then you see the last human beside you. You'd want to graps on her/him no matter what. Especially if she can end your misery