Now, what did I miss?

Clearly, as you hinted by noting that studying certain subjects can actually make you dumber, the key problem is how to evaluate the soundness and reliability of the existing literature in a given area as an non-expert. I raised this topic many times on LW, including in a recent top-level article, but there doesn't seem to be much interest in it here -- even though the issue is, in my opinion, of crucial importance, not least because all the arguments about the value and importance of scholarship that you list also hinge on it.