Do you think he's out of his mind or does he make some very good points? I tend to agree with him. To clarify what his position actually is, it is not the claim that brain diseases don't exist, it's the claim that the bulk of contemporary psychiatric diagnosis do not constitute brain diseases and therefore are imaginary diseases made up to explain away undesired behaviors and put people on drugs.
In the absence of any objective medical evidence, much of contemporary psychiatric diagnosis, particularly as it relates to children, is kind of half-baked at best. Especially in the case of "recently discovered" (or invented out of thin air, in my view) things such as ADD. It seems like an excuse to put people on drugs and through theraputic programs. I'm willing to grant that a certain number of diseases of the brain have been discovered (ones that constitute an actual malfunction of the brain), but a lot of the ones that have popped up only in recent years warrant severe doubt.
Part of the problem is that mere eccentricity or behaviors outside of "the norm" are erroneously equated to mental illness. If your child is eccentric, they may very well be a genius, not a sociopath. What some psychiatrists are labeling as a "mental handicap" may actually be a blessing. I just don't trust the shrinks. I never have. Too many of them are taking advantage of their position as a means to control others and keep the medical-industrial-complex charade going.