Yep, those were the grand old days of psychiatry, when anyone with a psychiatric illness was assumed to be not only less intelligent but also less human, and it was thought that more than 75% of people with autism were also retarded.
The saddest part is that many psychiatrists practising today were trained during that time, or were trained by psychiatrists from that time. My own experience is that often the staff of psych wards still assume that the patients are not intelligent.
During my own treatment, I've had nurses refuse to give me the name of the medication they wanted me to take, or even give an explanation of it beyond "This will help you feel better"; also, I had a social worker tell me in front of a group of other patients that he knew that I "smoked pot and took lots of downers", and that he knew this not because of urine testing but because he could "just tell" from my personality. (For the record, I had been given a single dose of an opiate-based painkiller for a migraine headache in the week prior to my admission. I did smoke pot regularly at the time, but I still am disgusted that he really expected me to believe that he knew this based on my "personality".)
Sorry, didn't mean to turn this into a rant about my own experiences. In any case, that book is a sad insight into the reality of the prejudices held by many so-called "professionals".