"Suppose we had chosen to sit out WWII, while successfully defending our own waters and borders. A successful missile defense system. What would the world be like now? What if Japan had been smart enough not wake the sleeping giant and attack Pearl Harbor, but just busied itself devouring Asia? What if Hitler had decided not to declare war on us, and the rest of the allies were unable to talk us into joining them?"

Hmm, Japan would have probably evenually failed trying to occupy China. Maybe the evenual result would Japan being invaded BY China.
Germany would have defeated Russia, but again would have had a hard time trying to occupy Russia- and could have got England agree not to be at war with Germany (have cease fire and evenually a peace agreement). No one would have built a nuclear weapons. England would probably still not join the EU:). Generally a lot more people would died, and generally a poorer world. It's hard to say if America would have been worse off, economically. The question is when would Japan or Germany stop invading and how eager would they been towards genocide- their inability of controlling their occupied countries, could made them try to killing whole populations- that was their mindset- though of course it would do anything but cause misery, and "insane levels" of hostility. India might have become more united. Africa might have become more united. I think the final result would have been Germany and Japan would have been destroyed and these people throughly despised [with good justification]. Or Germany and Japan could restrained themselves, realizing the futility of the continued war, redraw a few maps and could have managed to kill fewer people than actually happenned in WWII. Again probably American would have about the same, maybe better off economically.
What would have happenned if instead of sinking battleships in Pearl Harbor, the Japenese had sunk them in the ocean- defeating rather doing a surprise attack? We might have looked at it differently- and the Japanese probably could have just as easily sunk those ships in the ocean as compared to being in a harbor, and btw killing more Americans than they did and, of course, the ships wouldn't have been recoverable.