This hypothesis lies close to the idea some psychiatrists hold that the paraphilias are simply another form of obsessive compulsive disorder (O.C.D.) and that the S.S.R.I.'s work not because they target sexual arousal but because they reduce ruminative thoughts and repetitive behaviors in all kinds of conditions. ''I hate that idea,'' Kafka says. ''The paraphilias and P.R.D.'s are not a form of O.