It seems like a big distinction between the two lies in how quickly they could be rolled out. A pre-WWII database of religion would have taken a long time to create, so pre-emptively not creating one significantly inhibited the Germans, while the US already had the census data so could intern the Japanese. But it doesn’t seem likely that not using facial recognition now would make it significantly harder to use later.
It seems like a big distinction between the two lies in how quickly they could be rolled out. A pre-WWII database of religion would have taken a long time to create, so pre-emptively not creating one significantly inhibited the Germans, while the US already had the census data so could intern the Japanese. But it doesn’t seem likely that not using facial recognition now would make it significantly harder to use later.