If you alter people's natural behaviour so that they are less manipulative, do you think this is the same as having not taken that action? It is a (further) unnatural intervention. It would be like giving someone an emetic because they ate too much.

The anti-manipulation training or the emetic could be beneficial, I agree.

The 'proper' answer would be to address the manipulator, to prevent their interventions, so that they can live their lives naturally, if they are not harming anyone.