Occasional mysterious death of volunteers before they get around to joyfully surrendering information. Expense of hiring professional counsellors. Less problematical if you have a local asylum for the criminally insane 2 . Difficulties in rapidly verifying false information. Mental stress caused to friendly counsellors by distressing language employed by some of their less stable subjects.
Some people also dislike the appearance and smell of intestines.
Data retrieval time must be significantly less than that of computational methods. Stress on personnel must be minimised. Maintenance costs should be low. These points will be addressed in turn and expanded below. Most useful voice recognition systems require a period of training before they can work effectively, this luxury may not be available.