Why schools should not teach general critical-thinking skills

Interesting critique. I'm inclined to agree. Having one good counterexample (or a lot of solid confirmatory examples) can often change your mind significantly. You can't accumulate this kind of information from first principals. That's why exploration is important, in the form of world experience and reading books. Travel does not broaden the mind because of physical geography, it does so because you realize vast numbers of people have a different frame of reference to yourself.

Without Darwin's visits to the islands and South America his ideas would have remained dormant. The same is true of reading a good book. You may have had those ideas before in some tangential form, but now you see them fully realized on the page. A single turn of phrase can make an idea click.

I also enjoy things such as The Sequences (general rationality heuristics), so it is a paradox.