He sighs. The man was too invested in the idea of evil librarians to see that it was ridiculous, just like Brittaninas mostly believed that blood and peerage was another term for merit. He simply could not bring himself to realize that the idea he had invested so much on was the babbling of a lunatic. It wasn't that the Evil Librarians were being manipulated, it was that he was being manipulated to think that the agency he was composing consisted of evil librarians.
"You are fighting a war. You cannot afford to choose your friends." Lelouch replies. "But if not him, there are plenty of others in a position to act on that information. Why not use one of them?"