That makes it sound like the Nazis allowed something like a "conscience clause", a practice our home grown anti-Lifers won't permit.
Rather disquieting to think Hitler could be more humane than Obozo.
I do remember reading that after the Roman Catholic Church strongly protested the euthanasia practices of the Nazis to remove “undesirables” such as handicapped and mentally ill people from the population, people who had been trained in those units were reassigned to the camps that eventually liquidated Jews and others.
It wouldn't surprise me if when the Nazis backed down, they decided it was best to use only volunteers for their death operations to avoid further conflict with Roman Catholics.
I'm not a Roman Catholic and I have no agenda to defend Catholics against Hitler, but liberalism had virtually wrecked the German Reformed and German Lutheran churches with the result that while individual Protestants stood firm against Hitler, the Catholic hierarchy opposed him in an organized manner to a limited extent while the Protestant denominations generally fell in line or were ineffective in organizing opposition.
It probably also helped that Hitler's Italian allies included many Roman Catholics who supported Hitler because of his anti-Communism and because of the anti-clerical nature of much of Italian liberalism, and at least during the first half of World War II, the Italians were viewed as being useful allies. Antagonizing Mussolini's friends would not have been a good move for Hitler.