It is all too easy to spend immense time learning and preparing how to teach something. Teachers can fail to question the value or accuracy of what is being taught. Certainly, it is better to fail at an attempt to teach the most valuable lessons than it is to succeed at teaching incorrect ideas.
The challenge of the most dedicated teacher is to balance these questions. People who spend all their time on the facts and ideas will certainly be lucky to have even a moderate ability to express them accessibly. On the other hand teachers can sometimes be so focused on how that they actually become more and more dogmatic, close-minded, and even defensive regarding "what" type questions. Those questions could undermine all the work they've done preparing the unquestioned subject.
Of course, we need to be practical. I would simply encourage all teachers and parents, (well, everyone actually) to try to return to what and why every now and then. And if those can't able to be answered with certainty and you can't afford the time to explore further, then at least keep the question open - allow for it to be questioned by others - and just don't teach it as absolute.
Students should not only question what and why but they need to remember sometimes to think about how things are taught. If a student questions how things are taught, then sometimes ideas that are poorly presented can be figured out anyway -- by understanding what is wrong with the teaching style. Or they can figure out how to learn for themselves. They may even empathize with the challenges the teacher faces. Finally, if they are like me, they may be inspired to become teachers themselves, if partly to do a better job than some of the teaching they received.
There is never anything wrong with questions. Everything should be questioned. We just have to realize that questioning everything means a very small proportion of questions are able to be answered. So instead of randomly questioning, we need priorities. If we ask the big what and why questions first, we'll have the best shot at everything else making sense later.