Economics Professor explains how cheaper housing will make America way more productive 

" move people from place with low productivity in country with hig productivity" what if we raise the producitivity of third world countries instead?

If there's a limited amount of space in the high productivity area, then it makes more sense to use that space on high-productivity workers than on low-productivity workers. Having high-productivity workers displace low-productivity workers is what's supposed to happen if we cannot create more space in the high productivity area (e.g. due to zoning).

Shocker…

These statements remind me of History and Philosophy of Science - that is when large sets of experimental data are found that refute the core hypothesis, auxiliary hypotheses are generated to save the core hypothesis instead of coming to the conclusion that perhaps the hypothesis isn't really supported by the data collected in the real world (see the Vulcan hypothesis to explain Mercury's orbit).

He forgot to mention how third world immigration turns first world countries into third world ghettos.

sounds good. but cheaper housing just allows people to spend more on status symbol objects.