the sparrow isn't connected to reality... this isn't Cersei he is dealing with... no he is dealing with someone who did the same as the Conqueror. And no it's time to follow Maegor' legacy - burn the cultists
This is the result of one religion having too much power within a state, it would be better for the king to have control and bring together several religions to oppose each other and create a balance. Of course, beliefs that harm the state should not be accepted.