Thanks for reading and commenting, Agnes.
I’m glad you’ve asked this question, because this is a confusing issue and one that’s almost never explained for the public, even as its ramifications are huuuge.
DSM is an attempt to codify human psychological maladies, and as such it contains all kinds of mental problems of varied origin (to the extent we can determine such), from organic brain damage to grief.
Mental illness in the general psychiatric understanding of the term (and there are nuances and such, but I will not try to address them for the sake of clarity) is the kind of mental disturbance that severely impairs a person’s functioning and contact with reality. So, for example, schizophrenia is a mental illness, as is paranoia, and also (severe) mania and depression. Mental illness is what earns a person an insanity defense in criminal court, because we know that when in throes of its symptoms, a person may not fully, or at all, understand the ramifications of his or her actions, and may not have full, or any, control over them because of his or her impaired judgment and self-control.
Personality disorders are not believed to impair a person’s contact with reality, judgment, and functioning. Although obviously this is debatable, given the cognitive and other distortions that form the core of these character problems, the impairment is not of the type and extent inflicted by psychosis. They do not cause hallucinations and delusions, for example, and a break with reality.
A person with a personality disorder — particularly psychopathic (which has been unfortunately turned into antisocial personality disorder in our current DSMs) and narcissistic — can and will function well in society. So well, in fact, that s/he will be enthusiastically (or not) elected to run organizations, companies, and countries (usually to the ground, given enough time). These individuals, unlike the mentally ill, are typically very well adjusted to societal mores, taking full advantage of people’s inability to spot and understand their character defect, that of an impaired or entirely lacking conscience.
One major problem with calling those who, like narcissists and psychopaths, are afflicted with character defects “mentally ill” is, apart from the clinical unsoundness of it, unfairness of that to mentally ill people who are, by and large, peaceful and decent folks, not causing damage to others, unlike those with character defects.
Unlike psychopaths, (chronically) mentally ill struggle with life and face significant stigma as a result. Narcissists and psychopaths are just the opposite: they are very effective at life and garner the respect of others because of it. Their impaired or lacking conscience helps in it.
Mentally ill tend to frighten and repulse others, while narcissists and psychopaths attract people to themselves.
Mentally ill appear bizarre and incomprehensible, while narcissists and psychopaths inspire (in too many people) admiration and a desire to emulate them.
Mentally ill get locked up and out of society, while narcissists and psychopaths easily rise in its ranks. Hitler, Stalin, Saddam Hussein and their likes would not be classified as mentally ill because they were / are not: they never exhibited any signs of mental illness (until late in life, when they became paranoid, and even that was not really recognized as an illness). But they were/are character defective — which is a better and more accurate term to use — and in the worst possible way, as they effectively lack a conscience.
Another ramification of this (mis)labeling confusion is our perennial — and willfully cultivated — cluelessness (or denial and obfuscation, more accurately) in gun control debates.
Whenever there is another mass shooting, we hear the calls about keeping guns away from the mentally ill. We do not want to talk about the fact that the mentally ill are, by and large, harmless, and that the mass shootings, like most gun (and not) violence, are overwhelmingly perpetrated by people with character defects (narcissistic and psychopathic, and combination of both). These individuals have no history of behaviors that would classify them as mentally ill — on the contrary, they tend to be well-adjusted, at least in superficial ways; and therefore have no history of psychiatric / psychological treatment. In fact, if you ask them and those in their close (but not too close) environment, you will hear what great fellas they are. If we manage to get a closer look, however, we always find signs of trouble brewing already: a pattern of non-criminal aggression dating to childhood, callousness and disrespect for others, lack of empathy and compassion, and a sense of specialness and entitlement.
To reiterate the point, narcissists and psychopaths are not mentally ill, although they are most definitely NOT mentally healthy or even normal. They are characterologically defective in ways that earn them a classification of personality disordered in today’s psychiatric nomenclature, but those disorders are not the same as mental illness.
I hope this makes sense.