Great question! If it's illegal to film a public servant then it is illegal to verify they are actually serving the public's best interest. In particular if you catch a public servant performing amoral or otherwise corrupt behaviour there is no way to publicaly verify that. Further without explicit legal protections for things then it is easier for that action to be banned or otherwise made illegal. No protection is no protection. A corrupt public servant has a vested interest in misinterpreting law in order to prevent you from exposing them. Which is why Oklahoma's ban on filming police is still bad even though it is framed under the guise of protecting police from harassment