Self defense

The enemy within rhetoric is a fascist tool used by autocrats to keep public discontent down. Heydrich, when he was running the Sicherheitsdienst realized this is what kept the common NSDAP party followers loyal.

But it only works for a while. You can prolong the effect by arresting / containing / purging / disposing of undesirables ( untermenschen or lebensunwertes Leben ) in large numbers which his why the SD hunted and arrested felonious Jews (as they were tasked to do) but any Jews they could add onto their list. Compare the ICE program to arrest and detain immigrants in the US, where they were tasked only to go after felons, but disregarded that qualifier, overwhelming their detention centers, yet allowing disease and filth to spread among the contained population.

Another method to prolong the effectiveness of enemy within rhetoric is to expand the list of undesirables that are persecuted, to discover that opposing ideologies have penetrated into newly-suspected populations (see also the McCarthyism era, circa 1950s) which is why most Christians are ultimately in danger even in a Christian Nationalist movement, once a state religion is established, those denominations that count as acceptable will narrow until there is only one left, and even then some parishes will be determined to be insufficiently pious.

Similarly, after the July 20 plot failed to kill Hitler, about 7,000 arrests and 5,000 executions followed, though few of them were actually associated with the plot itself, rather were gadflies of the NSDAP party and the SS, ( society offenders who might well be underground / and who never would be missed / who never would be missed ) since politics in the German Reich was conducted with long knives.

Eventually there are more people in the population who are hiding an aspect of themselves from the state and their neighbors then are people who have nothing to hide, which makes a society fecund for organized criminal syndicates to arrange for protection from the state. (The Sicilian Mafia started as a counter to the Holy Inquisition, for example). But hopefully before it gets to this stage the Allies storm Berlin and the genocide engine is shut down.