The first mass killing, around 1934 or so, were of the healthy, but sever handicap, and even mildly retarded in Nazi Germany. That was an easy group with absolute few advocates, and somewhat well supported ideologically by the German opinion class.
Efficiency, scientific society, healthy breeding and all that...
Very familiar with those facts. Although I was ignorant to the current views. I thought they had learned their lesson. A couple of generations can reek havoc on our world. I forced myself to visit Dachau in 1984, quietly and tearfully trying to understand how man could do this to mankind.