That they did this is a fact. But why that should be the particularly egregious element in a systematic murder is a value judgement which you have simply stated but not bothered to explain.
Sorry, but your morality doesn't take automatic precedence just because it is yours.
It is unprecedented at the scale and sophistication that it was planned, organised and directed.
Nobody has ever built a structure with the sole and direct purpose of mass murder, other than the Nazis.
You know this of course.
I like how you love to play yourself as Schrodingers Nazi.
Use Nazi slurs ... no i am legitimately criticising everything on the planet as being Cultural Marxism.
Play coy with holocaust denial ... i need everyone to agree there were other genocides first and why is everyone oh so worried about this one specifically.
Factual evidence of the unprecedented scale of the Nazis genocide ... stalin starved people.