For people who have been diagnosed with a mental health problem, life serves up a number of hazards. Not least of these is the certainty that from time to time you will open a paper or turn on the radio to find yourself being discussed. I'm sure I should say "your diagnosis" as opposed to "yourself", but that's not how it feels, and I'm writing about how it feels. Diagnoses of mental health problems feel personal in a way that physical health problems don't. And no diagnosis feels more personal than that of a personality disorder.

With illnesses such as depression, schizophrenia and bipolar disorder, it is possible, to some extent at least, to feel oneself as distinct from the illness. You may experience recurrent "episodes" but will also have periods of stability when you feel, to coin a phrase, "much more yourself". But a personality disorder is precisely that, a disordered personality; the problem is not an illness, the problem is you. Not that it's a question of either or. Plenty of people, myself included, have been diagnosed with both a mental illness and a personality disorder. Double whammy.

I picked up a borderline personality disorder (BPD) diagnosis after a year and a half at a day hospital during which time my condition deteriorated so severely that I tried to kill myself. I was summarily discharged and the BPD was handed to me like a parting gift, an explanation as to why it was I had failed to respond to "treatment". One is tempted to suggest that it might be more helpful to diagnose the treatment than the patient who fails to respond to it. But ignore me, "inappropriate anger" is a classic symptom of a "borderline personality".

BPD is used to describe a cluster of symptoms including marked and persistent instability of mood; unstable self-image, often leading to chronic feelings of emptiness; a tendency towards black and white thinking; impulsive behaviours; fear of abandonment and so on. To be fair, I do recognise some of this, though I'm not going to tell you which bits. Harder to handle, is the stigma attached to the diagnosis, both inside and outside the medical profession and in the media.

In a recent article in the Independent, entitled Why a lack of empathy is the root of all evil (5 April), and illustrated with a photograph of a mass of skulls fractured in the Rwandan genocide, we are told that people with BPD "are capable of inflicting physical and psychological harm on others and are unmoved by the plight of those they hurt". The reason? Zero empathy. According to Simon Baron-Cohen, professor of developmental psychopathology at Cambridge University, and author of Zero Degrees of Empathy: A New Theory of Human Cruelty, behaviour usually described as evil can be better explained as resulting from a lack of empathy. People who lack empathy, says Baron-Cohen, see others as mere objects.

To the extent that the term "evil" is often used as a way to shut down an inquiry, a refusal to try to understand what can lead people to behave in appalling ways, I agree with Baron-Cohen. But this is a very far cry indeed from telling everyone diagnosed with BPD that they don't care about other people.

In an article in the Observer, The science of empathy, (27 March), Baron-Cohen writes on the same theme. He has been fascinated by evil, he tells us, since his father told him as a child that the Nazis turned Jews into lampshades. "People said to be 'evil' or cruel are simply at one extreme of the empathy spectrum. We can all be lined up along this spectrum … based on how much empathy we have. At one end of this spectrum we find 'zero degrees of empathy' … There are at least three well-defined routes of getting to this end-point: borderline, psychopathic and borderline personality disorders. I group these as zero-negative because they have nothing positive to recommend them."

There is a certain dark humour in finding such statements in a piece on empathy, but I can't say I'm laughing. I think I'm a pretty empathic person. But how would I know, after all? I know plenty of people with BPD and not one of them fits Baron-Cohen's description. But do I fit it? That's the question. Do I?

Clare Allan is an author and writer on mental health issues.