There’s a very good article on Eruditorum Press that talks about this phenomenon in the context of the TV show Merlin:

As ever, in Merlin, the oppressed and persecuted are both depicted as baser and nastier than anyone else and held to a higher moral standard. They must shut up and put up, and wait forebearingly in hope for reform, or they become malignant. To resist is to become wicked, by definition. Look what happens to Morgana. She discovers that she has magical abilities; she comes to empathise with people victimised by Uther’s regime; she becomes disgusted by Uther’s cruelty; she is approached by people fighting back; she eventually goes over to their side. But, of course, the druids and sorcerers she meets are cynical and machiavellian and cruel… because revolutionaries always are. Morgause uses and manipulates Morgana. She allies herself with a vicious warlord. She slaughters the innocent. Morgana’s ethical awakening, her rejection of the system from which she has previously benefitted, and her identification with the oppressed, is specifically shown to stem from empathy and moral outrage at injustice… and yet, somehow, without any rhyme or reason, when she finally departs Camelot and openly goes over to the other side, she becomes a sadistic psychopath with no regard for the suffering of the innocent, acting from motives of thwarted ambition, petty jealousy and irrational vindictiveness. Her political awakening comes from compassion and simultaneously nullifies that compassion. It couldn’t be clearer: political outrage, no matter how well intentioned, instantly becomes dangerous the moment it steps beyond the boundaries of the state, of the mainstream, of the legal, of reformism, of consensus political normality.