De-Nazification required the Allies mass-murdering about a million Germans after the war was over. There's a reason why there's a fudge factor of 1M in the POW camps in the years after the war.
During the Civil War, Abolitionists mass-murdered slave owners by way of dueling them. The story of Cassius Marcellus Clay is littered with stories of brutally killing slave owners and we champion Abolitionists as righteous.
De-Nazification as policy essentially evaporated in the west in the earliest years of the Adenaur government. Killing and displacement of Germans in the east certainly occurred, but the example of the west shows this was not essential.
Killing men in personal duels is not comparable or relevant.
My point being that it makes no sense for a society that just underwent Nazi occupation to let it continue.
After such a violent effort, it is a foregone conclusion that the remaining cancer is mercilessly destroyed. If you don't, then all of the lives sacrificed for the cause are meaningless.
What the West has a problem with is reconciling the inescapable reality that true believers absolutely must be killed (for good reason).
There is nothing within the Western view that affords anything short of death for these people. This makes people very uncomfortable, but it's necessary if Western civilization is to continue.
During the Civil War, Abolitionists mass-murdered slave owners by way of dueling them. The story of Cassius Marcellus Clay is littered with stories of brutally killing slave owners and we champion Abolitionists as righteous.