The point is that many diseases/disorders were unknown (or, "poorly understood") before the current state of modern medicine, and it is ignorant to claim/assume that these problems did not previously exist.

Well, the way you explain it, many diseases are still poorly understood.

What it boils down to, in my eyes, is the question if you take the viewpoint that certain diseases were "underdiagnosed" (because they were "there, but not understood") in the past versus the viewpoint that they are currently "overdiagnosed".

Combine that with the claim that much of the scientific literature, perhaps half, may simply be untrue.60696-1/fulltext?rss%3Dyes) (This is the Lancet, not some blog), and you get why people are so skeptical. From my anecdotal point of view, I would guess that for every 2 persons legitimately diagnosed with ADHD, one kid is misdiagnosed because parents and teachers are unable to cope with him/her. Doctors happily go with it, because they have financial gains.