"It really seems so obvious. If somehow the population were limited on Earth there would be enough resources, including education, for everyone. And then all the interesting stuff could be done.

And if the population isn't limited, the humanitarian and political efforts to calm a riotous underclass, both people and nations, will preclude much of the "fun" stuff. And it will only get worse.

I don't know why that is so hard to see, I really don't."

Maybe it's hard to see cause there is no evidence which support either of these assumptions?
You might find some evidence of where populations were unlimited, then that's when all the interesting stuff can be done. Or where populations were limited, it only got worse. Though not sure you could find enough to give any definite conclusions.
Now, we have two countries China and India both large, dense populations, China is systematically trying to limit it's population- perhaps some evidence could be found by closely examining these countries.