What excuses the governments action for infecting 1,500 Guatemalans with syphilis? How should it be justified?

Obama recently called the President of Guatemala and formerly apologized on the behalf of the United States Government for the testing of 1,500 Guatemalan patients and prisoners in mental hospitals by infecting them with syphilis during the 1940's. This raises more questions than answers: Has there been other experiments run by the government that we don't know about? ex. HIV, H1N1..What is the govt. real objectives and why?