It is, without doubt, shocking that a public idealist like Arthur Miller – who in his plays and campaigning was a champion of the underdog – should privately have so callously disposed of his own son because the boy was born with Down syndrome. Miller had the week-old baby sent to an institution and then to a school for the mentally retarded, keeping the boy's existence so secret he was not even mentioned in his autobiography.

It would be wrong to condemn the writer totally. For the lesson to be drawn is not solely one of a gap between public and private morality, with the imputation of hypocrisy. It is also a measure of how far social attitudes have shifted since Danny Miller was born in 1966, just seven years after the discovery that the condition was caused by an extra chromosome and when the official diagnosis was not Down syndrome but "mongolian idiocy". Indeed, it was only in 1965 that the World Health Organisation dropped the term mongolism, and not after protests by parents but after a request by the Mongolian government. In the UK it was not until 1971 that the law was changed even to require an education for such children.

When Danny Miller was born, the standard advice was that it was kinder and safer for the child and for his family if he was cared for in an institution. Today, things are different. We understand that this is not an infectious or degenerative disorder. Children with this learning disability can, with the correct support, thrive. They can, with a mix of special education and mainstream schools, happily learn to read and write, and can participate in a wide range of leisure activities. They pass GCSEs and can, with supportive employment and housing environments, live full, semi-independent adult lives.

Sadly, ignorance and prejudice remain widespread, however. At the most extreme level, this was shown in three recent disturbing court cases, where a man with learning disabilities was tormented in a shed, another pushed from a bridge and a third brutally battered to death by vicious bullies. There is the lack of employment opportunities for people with disabilities and the closing down of special schools. Or even just the looks, the stares, the patronising comments that are so much a feature of daily life for disabled people. Rather than being shocked by Arthur Miller, we would do better to turn our startled scrutiny on to our own times.