The prosecution and the execution of Jews and other (what the Nazi's deemed as) 'less superior' races (Roma (Gypsies), disabled, homosexual, Jehovah’s Witnesses, etc.) is not what makes this story unrealistic. What to some people might be unrealistic, is the miracle given to him by G-d, some people might find this unrealistic, while others might not. Personally I do believe in the fact that G-d gives miracles, but for the fact that this is not unanimously agreed upon, I am considering this to be unrealistic.