[kragen]

you have a point. while biology textbooks might be controversial among creationists, and physics textbooks might be controversial among flat-earthers, in mainstream society the only thing controversial about them is the idea that they're worth devoting attention to

on the other hand, if the authors of the textbooks don't have any controversial ideas, they probably aren't qualified to write the textbooks and will fill them with their half-understood memories of what someone else told them, which is more likely than not false in the first place. (examples abound: https://www.washingtonpost.com/archive/politics/2001/01/16/1...) ideally you want the authors of your textbooks to habitually practice the kind of critical thinking that will enable them to avoid filling the textbooks with errors, and which also guarantees that they will have controversial opinions

case in point: you're a lot better off learning chemistry from linus pauling's physical chemistry than from 95% of current textbooks, both because it's better written and because it's better thought out and more carefully written. as far as i can tell, the book doesn't have any controversial opinions in it, but pauling notoriously did; at some point he became convinced megadoses of vitamin c were great for your health. i'm pretty sure he was wrong about that, but at the time it was controversial