History's most vivid example of social engineering of this form was fascist Nazi Germany's final solution, essentially the total eradication of Jews by organized mass murder or genocide. Other groups of people Nazi Germany deemed not fit to live or exist as equals in an Aryan society included the mentally retarded and physically disabled, homosexuals, gypsies and other minorities and nationalities. By the end of The Third Reich it had killed outright several million healthy people solely on the basis of their undesirable ethnicity, sterilized 460,000 people deemed unfit, disturbed or asocial killed 250,000 chronically ill individuals by starving, gassing or poisoning them and gassed 10,000 babies and children who suffered from a variety of disorders. More recently, fascist "ethnic cleansing" has been used as a doctrine in ex-Yugoslavia to purify regions from other ethnic groups by murder and terror.
Society must face the concept that we kill off the old, weak, the stupid, the inefficient. A piece of meat in the shape of a man but without a mind is not a human being, whether the body be deathly ill, damaged by accident, mentally blank because of brain deficiency, or criminally insane.