Jews were not trying to kill civilians in their host countries, Corkie.
Now that Syria has been pacified by, of all people, the Russians, why do they need to leave?
The civil war in Syria is essentially over except for a few places still controlled by ISIL, as BO likes to call it.
European Jews in 1938, the year of the SS St.Louis were educated, skilled, wanted to come as families, were fluent in European languages, and had no desire to demand special rights. Cokie is correct, FDR should have allowed them to enter.