What would have really happened?
I grew up around relatives who had to put their lives and dreams on hold when they were drafted into the Army to fight the Nazis in Europe and others who waited at home fearful of never seeing their brothers or husbands again so I have some idea of what the American mindset must have been like during the Second World War. I've also read old accounts of that era where people were attacked, often physically, for belly aching about gas and meat rationing, hoping the war would go on longer, because they had a good job at a defense plant and other insensitive remarks in front of people with relatives in harm's way. Given all this I wonder what would have really happened, back then, to theater patrons who cheered for the Nazis, during a movie, as happens in "Focus". At the very least someone who did that would get a a soft drink or a cup of popcorn thrown in their face and, at worst, would wind up in the emergency ward.
The film is set in the New York City area where not only members of the Jewish community, but also Poles, other Eastern Europeans, Greeks, Italians and others who had relatives in Nazi controlled areas would be in the audience in most theaters. They definitely would not put up with such behavior. Also there is the subject matter the film; playing at the theater. While a few movies of the time, like the "Seventh Cross" hinted at anti-Semitism in Nazi occupied Europe none depicted genocide. The scope of the reality was too great, even among those who knew, to believe, much less make a movie about, until the death camps were liberated and the unspeakable truth was reveled for all the world to see. While the theater scene does fit in with the movie's theme of anti-Semitism it isn't true to the time when it is set.
Just remember: I was as good as any and better then most-Vincent Freeman in Gattaca