One of the problems with authoritarianism is that even though most dodgy Daves will be fine because the political apparatus doesn't have the time or energy to arrest everyone for everything, they retain the ability to arrest anyone for anything.

The moment your dodgy Dave offends your local cadre, even for reasons entirely other than being dodgy, they'll throw the book at him. And because there is now unpredictability around who will be arrested and for what reason, it acts as a chilling effect for everyone who values some degree of stability in their lives. So the arc of dodgy Daves bends toward compliance.