I seem to recall that one of the cornerstone factors in determining whether something was a mental "illness", rather than just some type of mental activity that can be categorized, was that it "interfered with basic/important life functions." It seems the DSM catalogs not just "illness" but all sorts of mental issues that are merely "discernible" without necessarily interfering with basic life function. This feeds into two other problems -- in modern society with its incredible range of life situations, something that is 'normal' or 'not a problem' for one person can be crippling for another. Secondly, the public has a love/hate relationship with mental diagnosis/labels. For every person lobbying for inclusion of a new "illness" in the DSM there are 5 who think all of psychiatry is overblown.

As an example, take "math anxiety." If you are a math professor who is expected to do/teach math every day in front of hundreds of students, then this might be a crippling issue. If you are an English professor whose spouse balances the checkbook, it might be a non-issue. The complication is that as 'society' evolves, then so do our ideas/definitions of mental illness. People who could have functioned just fine in simpler/slower times are now regarded as "ill" or "disabled", not just by lack of general intelligence but also because of behavior 'quirks' that may have once been eccentric but are now crippling - preventing employment, etc. This is reinforced by the increasing usage of 'screening' by employers (and even social relations). People who are "odd" or "moody" are increasingly finding it hard to even get jobs. They demand to know why they can't make a living (you are sick!) and the companies need a 'scientific' reason to not hire people (they are sick!). Thus, the DSM can become a self-reinforcing cycle of justification for social sorting.

Things that were only a few years ago absolutely "normal" are now raising eyebrows. A teen recently asked me if I had "a fear of surgeons." I wondered why he would even ask me such a thing. "Because you wear glasses, and haven't had your eyes fixed. I figured you must be afraid of surgery." It had never ocurred to me that wearing eyeglass might already be a symptom of some kind of medical phobia. Another person half-jokingly called me "anti-social" because I don't normally carry a cellphone. Is it now "anti-social" to not want to be called at all hours? The simple truth is that since we define mental illness largely by how it impacts our ability to interact with the world -- as the world changes ever more rapidly so do our mental illnesses. And thus the DSM may reflect less the 'scientific reality' of brain chemistry, etc. but more the 'social reality' of how our world is organized.