I think a lot of dystopias arise from Rousseau-style or blank-slate naturalism - the idea that humans are naturally good (or that they can be easily socialised

I think a lot of dystopias arise from Rousseau-style or blank-slate naturalism - the idea that humans are naturally good (or that they can be easily socialised to be naturally good). A dystopian ruler does not believe they are destroying humanity, they believe they are rescuing humanity from some exogenous menace, whereas a more Hobbes-inspired ruler believes themselves to be rescuing humanity from itself. If humans are only evil because they are brainwashed by capitalism, or patriarchy, religion, or royalty, or lizardmen, or the government, or some other menace then any brutality used to purge this evil is both justified and a temporary state of affairs. On the other hand, if you assume that some people are just a little bit naturally anti-social then trying to fight this (through either soft measures like education, or hard measures like punishment) is only justified if the the tangible benefits (not the promise of some eventual Utopia) exceed the costs.