the walls of psychiatric institutions, but as suggested by others in this thread it may also have been motivated by outrage about the psychiatric institutions themselves
That inmates were (and sometimes still are) mistreated is commonplace knowledge now. But the nature of the outrages was not so well-known then. Frederick Wiseman's 1967 documentary
Titicut Follies, probably the only film ever actually banned in the US, exhibits treatment of patients (at the Bridgewater Hospital in Massachusetts) that will seem entirely familiar to Kesey's readers. See
http://en.wikipedia.org/wiki/Titicut_FolliesLobotomy was still a common procedure when Kesey's book was published, though there was growing concern. The Soviets had banned procedure a decade earlier. As a "therapeutic" intervention, after destroying perhaps 100K lives, it largely vanished worldwide before the end of the decade. See
http://en.wikipedia.org/wiki/LobotomyThe subtext, that the staff of the hospital are not competent to judge who is sane and who is not, later became the topic of some professional study. Rosenhan, for example, carefully arranged for a number of perfectly normal people to be admitted as patients to psychiatric institutions, and showed that staff would then interpret the most ordinary behaviors as symptoms of mental illness:
Science 19 January 1973:
Vol. 179. no. 4070, pp. 250 - 258 ...
On Being Sane in Insane Places
D. L. Rosenhan 1
1 Stanford University, Stanford, California 94305
It is clear that we cannot distinguish the sane from the insane in psychiatric hospitals. The hospital itself imposes a special environment in which the meanings of behavior can easily be misunderstood. The consequences to patients hospitalized in such an environment—the powerlessness, depersonalization, segregation, mortification, and self-labeling—seem undoubtedly countertherapeutic ....
... Clearly, to the extent that we refrain from sending the distressed to insane places, our impressions of them are less likely to be distorted. (The risk of distorted perceptions, it seems to me, is always present, since we are much more sensitive to an individual's behaviors and verbalizations than we are to the subtle contextual stimuli that often promote them ... ) ...
I and the other pseudopatients in the psychiatric setting had distinctly negative reactions. We do not pretend to describe the subjective experiences of true patients. Theirs may be different from ours, particularly with the passage of time and the necessary process of adaptation to one's environment. But we can and do speak to the relatively more objective indices of treatment within the hospital. It could be a mistake, and a very unfortunate one, to consider that what happened to us derived from malice or stupidity on the part of the staff. Quite the contrary, our overwhelming impression of them was of people who really cared, who were committed and who were uncommonly intelligent. Where they failed, as they sometimes did painfully, it would be more accurate to attribute those failures to the environment in which they, too, found themselves than to personal callousness. Their perceptions and behavior were controlled by the situation, rather than being motivated by a malicious disposition. In a more benign environment, one that was less attached to global diagnosis, their behaviors and judgments might have been more benign and effective.
http://www.sciencemag.org/cgi/content/abstract/179/4070/250