This is indeed interesting, thank you. As it happens, I'm currently reading "Intellectuals and Society" by Thomas Sowell, and there seems to be significant overlap with what Johnson writes. Sowell points out two main characteristics of intellectuals: what they say is not subject to external standards of verification but to internal standards among the "intelligentsia". In other words, it is their business to make claims that go beyond their actual expertise. And, importantly, they are "ultimately unaccountable to the external world".