I think part of it is the sense that Jews for the most part are productive people who make contributions in all areas...however, some of the hesitation may have been based on the perception that many were adherents of socialism.
In other words, George Orwell's immortal quip in Animal Farm that all animals are equal, but some animals are more equal than others? On purely humanitarian grounds, I'd say there was no reason to privilege Jewish refugees over the many victims of genocide that include the Armenian and Ukrainian ones over the course of the 20th century. An Armenian or a Ukrainian might say "there are so many non-Armenians and non-Ukrainians in the world - you could kill hundreds of millions of them and still have plenty left over - why not save us first", but that, like this author's view, would represent a purely parochial argument.
I would think that would all the more reason for FDR to help them.
Doubt it. Given FDR's views on how society should be organized, that would have been a reason to import as many as possible.
But the thing was, FDR was not that smart. His milieu was anti-Semitic, and he acted on his evil instinct, understanding that his execrable base might have reacted negatively to such a move towards diversity (was that word even coined yet?).