"He worries. We all do. I'm worried that sometimes, you're too like me in places where you should be... not. I have a feeling that he feels the same way. He is wary of you, Ariel, as he is all of us. He knew I'd fall before I did. He knows what the seeds of corruption look like before they're even planted, and worried that you could not overcome the ones I planted in you back then. We're all worried about that, but I doubt he spent long distrusting you, if he did at all." He shook his head, "However, I must stress to you that loving outside of our kind is not a reason any of us have fallen. Love is the basis of our doctrine, of our very existence. No; it is putting that desire for whatever they've become impassioned about before our duties that the Grigori fell. Bearing children has nothing to do with it, either, at least not specifically."
He'd looked into it in Qing's vast library since it had also been a point of confusion for him.