I also like Leto II's conversation with Moneo about rhetorical despotism:
God Emperor of Dune wrote:"Religion always leads to rhetorical despotism," Leto said. "Before the Bene Gesserit, the Jesuits were the best at it."
"Surely you've met them in your histories?"
"I'm not certain, Lord. When were they?"
"No matter. You learn enough about rhetorical despotism from a study of the Bene Gesserit. Of course, they do not begin by deluding themselves with it."
The Reverend Mothers are in for a bad time, Moneo told himself. He's going to preach at them. They detest that. This could cause serious trouble.
"What was their reaction?" Leto asked.
"I'm told they were disappointed but did not press the matter."
And Moneo thought: I'd best prepare them for more disappointment. And they'll have to be kept away from the delegations of Ix and Tleilaxu.
Moneo shook his head. This could lead to some very nasty plotting. The Duncan had better be warned.
"It leads to self-fulfilling prophecy and justifications for all manner of obscenities," Leto said.
"This... rhetorical despotism, Lord?"
"Yes! It shields evil behind walls of self-righteousness which are proof against all arguments against the evil."
Moneo kept a wary eye on Leto's body, noting the way the hands twisted, almost a random movement, the twitching of the great ribbed segments. What will I do if the Worm comes out of him here? Perspiration broke out on Moneo's forehead.
"It feeds on deliberately twisted meanings to discredit opposition," Leto said.
"All of that, Lord?"
"The Jesuits called that 'securing your power base'. It leads directly to hypocrisy which is always betrayed by the gap between actions and explanations. They never agree."
"I must study this more carefully, Lord."
"Ultimately, it rules by guilt because hypocrisy brings on the witch hunt and the demand for scapegoats."
The cortege rounded a corner where the rock had been opened for a glimpse of the bridge in the distance.
"Moneo, are you paying close attention to me?"
"Yes, Lord. Indeed."
"I'm describing a tool of the religious power base."
"I recognize that, Lord."
"Then why are you so afraid?"
"Talk of religious power always makes me uneasy, Lord."
"Because you and the Fish Speakers wield it in my name?"
"Of course, Lord."
"Power bases are very dangerous because they attract people who are truly insane, people who seek power only for the sake of power. Do you understand?"
"Yes, Lord. That is why you so seldom grant petitions for appointments in your government."
"Thank you, Lord."
"In the shadow of every religion lurks a Torquemada," Leto said. "You have never encountered that name. I know because I caused it to be expunged from all the records."
"Why was that, Lord?"
"He was an obscenity. He made living torches out of people who disagreed with him."
Moneo pitched his voice low. "Like the historians who angered you, Lord?"
"Do you question my actions, Moneo?"
"Good. The historians died peacefully. Not a one felt the flames. Torquemada, however, delighted in commending to his god the agonized screams of his burning victims."
"How horrible, Lord."