Nazi Germany provided people the opportunity to become an extremist by answering a job ad, and put together a whole murderous infrastructure of extremism in about a decade.
That's certainly not true. They perhaps didn't know the full details, but Hitler was very clear about his intention to eradicate Jews from Europe even in 1939 when the Holocaust had barely started.
They definitely knew that Jews were being rounded up and sent to camps for slave labor in horrid and dangerous conditions that would kill many of them.
