"Psychology, which explains everything
and we are still in doubt."
Marianne Moore, from "Marriage"
By "we" I don't mean we psychiatrists, at least not primarily, but rather "we the people." Caseness, or the determination of what counts as a mental disorder and what doesn't, is not something we go out and discover in nature; rather, it is a social category arrived at both explicitly and implicitly through cultural debate. The psychiatric profession obviously has opinions about caseness, but these do not go unanswered or unlimited by society at large.
In large part, antipsychiatry critique has been aimed at the extent of psychiatric diagnoses, both the numbers of diagnoses themselves (larger in every succeeding edition of DSM, we are reminded) and of course the numbers of people given those diagnoses. Suddenly it seems as if every other kid has ADHD and/or autism. Recently several psych blogs cited a recent survey claiming that 38% of a European sample suffers a mental disorder in a given year. This included substance abuse and dementia, but nonetheless it seems like a high number (the 5 or 10-year prevalence would be significantly higher).
I think that 38% seems like a high number for reasons both illegitimate and legitimate. Even now there is a tendency, more latent in some than others, to view those with mental disorders as the mad, an appalling but surely very minority group safely stowed away in institutions. The notion that "the mentally ill" walk the streets and even have jobs and families like you and I remains foreign to some. But there is also the real concern that the sick role, a transaction that officially relieves the patient of at least some social responsibility, loses its meaning when used too widely. In that respect, there is too little appreciation of the great variation in severity of mental disorders; just as one may go to an internist for a touch of gastritis or for cancer, a technical psychiatric diagnosis may or may not involve significant disability or the use of the sick role.
Whether medical or psychiatric, diagnosis when applied liberally enough approaches the condition of enhancement. For Freudians neurosis was an inescapable condition of humanity, so at certain times and places (and with sufficient economic resources) to be in analysis did not mark one as "sick" so much as self-aware and ambitious. Similarly, in those older than 85, significant dementia is closer to the rule than to the exception, so statistically speaking the effective treatment (which we don't yet have) of dementia in the very old would in fact qualify as enhancement. And for modern medicine, mortality itself has virtually become a disease (which as the Onion occasionally reminds us, retains its 100% prevalence despite our best efforts). When we seriously discuss mental disorders having a prevalence greater than 50%, we start to consider syndromes that are, in toto, to be expected of the human condition, at least at this place and time.
Enhancement may well be justified, depending on the circumstances. The question is always: is treating any given phenomenon clinically (that is, as a syndrome worthy of specific medical intervention) likely to be helpful (that is, to lead to better functional outcomes, in the case of those problems for which we really do have treatments, or to better understanding of ourselves and others, in the case of those problems that remain intractable)? Or would it be better to consider the issue as a social/moral/cultural/existential difficulty? That is really the question, and not one that neuroscience can shed any light on whatsoever. Biologically, all human capacities appear to exist on dimensional continua, and the point at which we indicate "pathology" or "caseness" is a social and interpretive outcome.