This diagnosis is not ‘labelling’ a person, but enabling them and others to learn and understand how differently the individual with autism sees things and to make adjustments to ease their passage through the world (which is not designed to be a comfortable or easy place for anyone with autism).
We don’t think of it as labelling to explain that someone is colour blind, but a helpful piece of information. So instead of becoming impatient with the colour-blind child as they persist in failing the colour-sorting task and insisting they do it again until they get it right, we realise that this task is not within their power to achieve without support. We realise that we then need to teach the child strategies for times when it is important that distinction is made between colours (eg; the sequence of traffic lights).
Even today, with all the increased knowledge about autism, I read a letter from a CAMHS psychiatrist which still clearly shows a lack of understanding that autism is by definition a developmental disorder, so that the difficulties experienced by his patient must be understood in the light of the diagnosis of autism rather than a personality disorder resulting from life history and events.
You cannot understand the person with autism unless you understand what autism means – a different brain, processing differently from the ‘norm’. To read autism as a personality disorder is not only unhelpful for the clinician as little progress will be made, but can be damaging and confusing for the autistic individual themselves.
I suspect that many individuals are misdiagnosed as Borderline Personality Disorder and other conditions because too few clinicians are familiar with the (however subtle) profound differences inherent in autism.