He has a point -- to an extent. We tend to pathologize a lot of fairly normal behaviors. This is especially problematic in children, where a label can shape identity for a lifetime.
However, as cognitive neuroscience continues to grow, we are learning that some things, such as ADHD, are actually brain chemistry dysfunctions, which fits even his definition of a disease.
The question then becomes -- and I think no one is really looking at this -- what is normal? Boys are diagnosed with ADHD at much higher levels than girls. But maybe boys just have less focused attention in general, and maybe this is a normal part of development.
There are some tough questions we need to be looking at as neuroscience begins to take over the field of psychology. We need to tease out in more detail what is adaptive and normal, even if it doesn't fit what we want to see, from what it truly not healthy in terms of who we are as human beings.
The failure to do this will result in a chemical version of Harrison Bergeron, where "everyone is finally equal."