It's particularly the mention of Jews here that makes it clear that in your view, the Nazis' racism was merely a matter of expedience, not conviction.
After all, would it not have been "convenient for the cause" for the Nazis to make all of Europe's Jews "honorary Aryans", and thus save themselves the trouble of murdering six million of them? The reason that they didn't do this is - obviously - that racism and anti-Semitism were a core part of their cause.
>White supremacism certainly didn't make Japan invade China.
A red herring, surely. We're talking about the cause of the war in Europe in this context. But in any case, there was certainly a racist component to Japanese nationalism too.
>nationalist expansionism
The Nazis' nationalist expansionism was intimately connected to their racism. Hitler invaded Poland so that racially inferior slavs could be replaced by racially superior "Aryans".
I just think it seems overly simplistic to the point of being almost nonsensical to say that WW2 was caused by white supremacism. White supremacism certainly didn't make Japan invade China. While I'm no expert, at the very least I can say that the Wikipedia article for "Causes of World War II" seems in agreement with what I said— while racism played a role, facism/militarism and plain old nationalist expansionism were much bigger factors.