No one actually believed immigrant Jews admitted to America in the run up to WWI and WWII posed a risk to kill Americans.
The “perils” “M” quoted were not about risk to American lives posed by immigrant Jews. It was about the perils dirty Jews posed to good Christian Americans.
A Nazi could have attempted to pretend to be a Swiss Christian if posing as a Jew wasn’t available. It has nothing to do with being Jewish. And you can ban Communists, including Communist Jews and Christians, without targeting Jews.