In its narrowest sense, "mentally disordered offender" refers to the
approximately twenty thousand persons per year in the United States who
are institutionalized as not guilty by reason of insanity, incompetent
to stand trial, and mentally disordered sex offenders, as well as those
prisoners transferred to mental hospitals. The real importance of
mentally disordered offenders, however, may not lie in this figure.
Rather, it may reside in the symbolic role that mentally disordered
offenders play for the rest of the legal system. The 3,140 persons
residing in state institutions on an average day in 1978 as not guilty
by reason of insanity (see Chapter 4), for example, are surely worthy of
concern in their own right. But they represent only 1% of the 307,276
persons residing in state and federal prisons in the same period (U. S.
Dept. of Justice, 1981). From a purely numeric point of view, the
insanity defense truly is "much ado about little" (Pasewark & Pasewark,
1982). The central importance of understanding these persons, however,
is that they serve a symbolic function in justifying the imprisonment of
the other 99%. The insanity defense, as Stone (1975) has noted, is "the
exception that proves the rule. " By exculpating a relatively few people
from being criminally responsible for their behavior, the law inculpates
all other law violators as liable for social sanction.