If it were true, why did the Germans stop killing the jews? Why did Germans not start killing the jews much earlier? Why is that when you meet someone from Germany now, the chances of them showing any enthusiasm for killing jews are vanishingly small?

Since Germans are still German, and presumably some even take some pride in being German, it's obviously possible to be German without - inexplicably - feeling any need to go on a jew-killing rampage.

On the other hand, if you find yourself some Nazis, or their fascist equivalents in other countries. I suspect they'll be much more enthusiastic about jew killing.

Fascism is a process and a social pathology, not a nationality. It's a pathology which doesn't just try to farm hatred for out-groups for political power, but also ends in self-destruction for the fascist order.

The Nazis didn't just kill the jews, they also killed their own vision of Germany, and millions of Germans with it. That's what fascists and authoritarians do. They don't just legitimise the murder of out-groups - given enough time and enough opportunity they'll lead any country or group into collective suicide.