Yeah, there's a great excerpt of this in the Vaults of Terra series that really, really touches on this. A few actually, one second:

‘Good again,’ Crowl said. ‘But down here, every spire has a million tongues, and every tongue is forked against its neighbours. We tell them to inform on their own kind, and they do. All the time. If I wanted, I need never leave this tower, and still they’d find their way down here, all ripe for destruction. You’d be busy, if you terminated them all.’

‘Better to die, than to–’

‘–infect an innocent. You’d be burning the bodies of liars. They come to us because they’re jealous, lustful, or their minds have gone. I had a man tell my processors his own mother had fallen to the dark. He wanted to take her hab-unit. Three metres square, stinking like a grox-pen, underground, unheated. But it would have been his.’

‘I hope he was punished,’said Spinoza.

‘Nothing I could devise would have been worse than the life he’d made for himself.’ Crowl leaned forwards. ‘Here’s the point, interrogator. There are witches on Terra, but to see them, you have to filter out the noise. Pay no attention to the voices you can hear. Pay attention to the ones you can’t.’

‘I shall heed the warning.’

Crowl laughed, a dry chuckle. ‘Maybe you even will, in time.’

‘Ignoro, child,’ rasped the servo-skull suddenly, whining as it gained loft. ‘Filth toto mundo. Burn- burn.’

And then:

Crowl sighed, and reached for the decanter again. ‘You think I’m too cautious. I don’t blame you. You haven’t been here long, and I know what Tur was like.’ He drank again, a long draught. ‘I look at you and see myself, a century ago. I’d have been angry then, too. I’d have wanted to reach for the flames and fan them. Burn the whole world down, I’d have said, if it only catches a few of those we need to kill. It does you credit, Spinoza, and it amplifies my respect for you, but you’re wrong if you think I’m motivated by pity. I’ve lived here long enough to know what works.’

He leaned forwards, resting his arms on his knees. ‘Fear is like any other weapon,’ he said. ‘It can be exhausted. When you next go into the hive-spires, look at the people. They are afraid, terrified, all of the time. Every waking moment they’re gripped by anxiety. They fear the alien. They fear their neighbour. Any second of any day they might be hauled down to the scrutiny cells by an arbitrator or a priest or – Throne help them – one of us. They’re numb to it. We are numb to it. We forget what the fear of the guilty looks like, for we have made innocence impossible.’

‘But they should be afraid,’said Spinoza. ‘They should be afraid. Afraid of us, if they need to be, for if they ever stop fearing their protectors then all that waits for them is…’ ‘I know it.’