Well, we aren't euthanizing them yet. The Nazi doctors initially began their work on the 'Final Solution' by moving the mentally afflicted out of institutions and into group homes.
From Robert Jay Lifton's book, The Nazi Doctors: Medical Killing and the Psychology of Genocide
Killing the infirm and mentally ill started in Europe long before the Nazi's ever came to power. And it is going on today in Europe. My wife - a cancer survivor - would not last long with these type of people in charge. Neither would any other cancer surviviors. As they say in Europe - no life for you! Next!