Case in point: von Neumann suggesting launching was the right strategy. I don't think anyone would argue today that he was right, though back then the decision must have seemed pretty much impossible to make.

Survivorship bias. There were some very near misses (Cuban Missile Crisis, Stanislav Petrov, etc.), and it seems reasonable to conclude that a substantial fraction of the Everett branches that came out of our 1946 included a global thermonuclear war.

I'm not willing to conclude that von Neumann was right, but the fact that we avoided nuclear war isn't clear proof he was wrong.