I'm sure you know this, but "WWII" is not a verb. The United States did not decide "to WWII" instead of "not WWIIing".

Japan aggressively invaded neighboring countries for resources and engaged in ethnic cleansing. The United States imposed a gradually more strict embargo of military and dual-use materials, including eventually oil. This precipitated the Japanese invasion of the oil rich Dutch East Indies and the attack on Pearl Harbor to cover for it.

If the question is "What should Japan have done?" the answer is "Not try to conquer Asia and not attack Pearl Harbor." If the question is "What should the United States have done?" the answer is not "Not try to conquer Asia and not attack Pearl Harbor." The answer might be "Disband the Pacific Fleet," or "Pay Japan not to invade its neighbors," or "Ally with Japan against Britain," or "Preemptively invade Japan," etc., but if you're trying to direct Japanese fleet movements or German concentration camp policy or the like, you're not engaged in an exercise showing the United States should have done anything differently.

Yeah, but were these oppressive empires really engaging in largescale genocide before WWII or was it (partially) caused by WWII? If I remember correctly, before WWII the "final solution" was supposed to be the Madagascar Plan, not The Holocaust.

The Madagascar Plan was never seriously considered, and when it was considered the war had already started (they were discussing it in 1940). People were already being placed in concentration camps in 1939. Moreover, the Madagascar Plan was a plan specifically for dealing with the Jews. The gays, Roma and other groups were not covered under that. Whether the Holocaust of the Jews was what the Nazi high command intended from the beginning is a matter of some debate. But given their general attitude even if Britain had quickly fallen, I have trouble believing that the Nazis would have stopped with putting all the European Jews on Madagascar, aside from the terrible loss of life that would have occurred in forcively adding millions of people to an environment with minimal infrastructure to support them.

Your point about the Soviet Union seems to be a valid one.

There is a more general problem here: There are some occasions where defensive wars need to be fought simply because if one doesn't then the enemy will wind up at your doorstep. World War 2 seems to have been such a war for much of Europe. That's less so for the US. But the overall point that having the war was better than the alternatives seems clear.

The technologies that were developed for the war are indeed impressive, but what of the technologies that would have been developed had WWII not occurred? How would we know if the seen outweigh the unseen in this case?

It's impossible to prove that WWII did not prevent the development of arbitrarily wonderful technology.

It is also impossible to prove that the Great Depression would have ended in the absence of an economic event like WWII.