I sympathize with those concerns. But yet there were many desperately poor people during the Dust Bowl / Great Depression era who somehow managed to migrate across the country in search of a better life. Why were they able to do it?
The Dust Bowl threatening people with starvation hardly seems comparable with high rents. If SF got hit by a natural disaster which destroyed the Tech community (analogous to farming as the main industry of the midwest), you bet people would leave.