[Jap2-0]

Sure, the subject matter is in the textbook, but that's not necessarily the only thing being taught—research skills (source evaluation, comparison, synthesis, etc.) also need to (or should) be taught at some point. And teaching material in multiple ways (and having student participation) is beneficial for learning and retention.

Now some parts of the case mentioned above obviously aren't great, but there are absolutely good justifications for this from an educational perspective.

[musicale]

As you suggest with source evaluation, there is something to be said for trying to teach some methods of verifying whether something is true (for some definition of "true") including methods for assessing (to some extent) the accuracy of various sources of information, finding information that may have been omitted, identifying underlying assumptions and viewpoints, etc.

Unfortunately, as dang has noted, fact checkers tend to find facts that support their position and to ignore or discredit those that do not. It's even a problem for scientists and researchers.

I still like the idea of a curated collection of sources.