As others have noted, teaching someone how to think and reason when teaching them helps keep things on the non-brainwashing side of things. That said, most of us have some beliefs (religious, political, economic) that we tend to view as strongly as those math ones, and consider them "truth" in a way that questioning them feels like an attack. I don't know if there's an easy answer about how to draw the line on those, since sometimes even discussing them just goes straight to our emotional lizard brains without ever hitting a logic circuit.