These are not an entirely US invention nor are they solely deployed in South and Central America.
The purpose is to destroy those who could become centres of opposition. Their victims may be innocent at the time, but sooner or later, they would get swept up into opposition to those in power.
Thus all "intellectuals", social workers, teachers, religious, jounalists not on board with the rulers, get the chop, by a bullet to the head or a fall from an airplane. They are often tortured for fun and to get information the rulers are too lazy to look up.
G'tmo is different, as that is a system for altering personalities and making them into turncoats.
Mr Negroponte is said to be the latest "go to" person.