This fascinating article says that even if textbooks portray one point of view, a teacher might still teach on an opposite view and ignore the one in the text. Yes, textbooks have many problems. The article ends with this sentence: Consequently I want to mention hubski contributor mpoe who has his students substantively edit Wikipedia pages. (Track him down and read his fabulous teaching philosophy.)
I imagine no one has answered your askhubski post because we can't remember most of our textbooks, and I suspect we are not really aware of the biases of our textbooks and the influence they might have had on us. But if you were aware of being shaped by textbooks, I'd like to know.A trip to Wikipedia by way of a smartphone will not necessarily let children work their way out of such dichotomies. But it will help.