I'm by no means an authority on the subject, but speaking from experience, I definitely used to be a midwit. I was one of those "NPR sweater liberals" (love that term) who just repeats whatever talking points the media presents and thinks himself informed for it.

This was my life from about 18-23. I think normal maturation is all that I needed to bring me out of it. If someone manages to cling to midwittery after 30 though, I don't have much hope for them.