Did they ever?

> At what point did the German people find it morally acceptable to start killing Nazis?

Late 1960s at the very earliest, and it's only been a tiny minority.

If it helps, the nazis themselves probably asked this very question before they started killing ... whatever the contemporary term for nazis was back than.

I don't think there was a label back then that was used the ways "Nazis" is used today.

Umbrella term for political opponents? Those always exist. Some variation of "jew puppet", if I had to guess.

Nazis isn't an umbrella term for political opponents

It wasn't until over a decade after the war that most Germans started to accept and internalize that the Nazis were bad guys.

There's also another war where the Germans think they're the good guys because it hasn't been a decade yet.

> At what point did the German people find it morally acceptable to start killing Nazis?

Functionally never, after the war the Allies handed "denazification" over to the West Germans to handle themselves in 1946. They then let basically everybody off and lots of former Nazis were let back into power. By 1957, 77% of the West German justice ministry was comprised of former Nazis, which was actually a higher percentage than the amount of Nazis in the ministry during Hitler's reign. The Soviets were more strict with the denazification of East Germany, but many former Nazis were still able to retain high positions in government and society.