The thoughts of a prisoner - they're not free either. They keep returning to the same things.
When the Nazis came for the communists, I remained silent; I was not a communist. When they locked up the social democrats, I remained silent; I was not a social democrat. When they came for the trade unionists, I did not speak out; I was not a trade unionist. When they came for me, there was no one left to speak out.
It is certain that the study of human psychology, if it were undertaken exclusively in prisons, would also lead to misrepresentation and absurd generalizations.