Aside from the 29 who disembarked in Cuba, that's back in Hitler's hands. Later than sooner, in the case of France, Belguim and the Netherlands, but the same eventual outcome.
Was it foreseeable that the Nazis would do an end-run around the impenetrable Maginot Line? That's certainly open to debate. But if the St. Louis passengers had been allowed entry into the United States, far fewer would have been murdered.
Something we can say easily in hindsight, but not something that anybody knew at the time. You can't blame anybody for not predicting that Hitler would conquer all of Europe before the Second World War actually started.
The German Jews from the St. Louis who wound up in France, protected by an army of 1.5 milllion, did not believe they were going to their deaths, and neither did anybody else.
But if the St. Louis passengers had been allowed entry into the United States, far fewer would have been murdered.
True but meaningless. They were illegal immigrants, other countries were willing to take them, and the US government didn't have many effective soothsayers at the time.