> "It's the engineers' job to resist with good reasoning. It's the visionary's job to convince them that we people only think the impossible things are impossible."

While I don't disagree with you, context matters greatly here. This is the same logic of every middle managing pawn or upper management narcissist who self-styles him or herself the "visionary" you describe. Someone like Musk has the technical aptitude and experience to accurately assess what is technologically possible or impossible and estimate how much it will cost and how long it will take. He has also surrounded himself with highly talented technical people who, from what I can tell, he listens to.

Unless someone has previously envisioned and brought to fruition some visionary product or service, we should remember that the most likely explanation for their insistence that the seemingly impossible is possible is some combination of their ignorance, incompetence, and narcissistic delusion.