4. Infecting Guatemalans with syphilis
During the Second World War sexually transmitted diseases became a huge problem for American military and their wifes. US government decided to study diseases like syphilis, gonorrhea to find more effective medicine. Instead of experimenting on already ill American soldiers doctors went to South America where intentionally infected thousands of Guatemalan military forces, prisoners and mentally ill people. Subjects of the experiment did not know about it therefore the illness spread very fast.