I agree. So would I. However, what Zed is doing in the last chapter is showing code written by other people. If you taught your students about an experiment done by other (widely regarded) researches, would you say "bad, bad, bad; they should never have used these chemicals"?
I would say: "See, they used it here, but only because they were very, very, very careful. Let's explore different ways this breaks down. … As you can see, I'd recommend you to not do what these people did."
Teaching people (especially in natural sciences!) to immediately disregard something, just to be safe, is not conducive to learning. Sure, at later levels, you can teach them the truth of things, but what if they don't get there?
Then you have a bunch of people freaking out over incomplete information that they learned in school, and influencing dumb policies (e.g., hooplah about nuclear plants).
Part of being a good teacher is recognizing that there are limits to how much you can expect a student to learn at a given level, and then making sure their knowledge is as "complete" as possible within those limits.