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Yep, it seems multiple factors are responsible.

I am not so concerned with resource depletion. We inhabit an insignificant layer of mist on the surface of a, rather large, relative to us, oblate spheroid in space. As large as is our planet, it is, itself, insignificant in relation to the vast amount of resources even in our solar system, let alone our local group, or our galaxy. It appears the universe is not exactly crowded. I would like to live to see it so.