NKVD means “People’s Commissariat of Internal Affairs”.

Internal Affairs. Yes. Internal to the Russian Communist Party.

Imagine if German police under Nazis and Gestapo were one and the same

The NKVD weren’t Jew-hunters, engaged in a policy of ethnic cleansing.

my knowledge of Stalinism is closer to the root, and Russian is my first language

You could say the same thing about Ayn Rand.

Their main activities were about organizing demonstrations on all the important days, though

You definitely sound very knowledgeable