[huevosabio]

> What's anyone's incentive for staying in... when bad things happen?

Well that's the beauty of it. Right now we are forcing (literally, by force!) people in war-torn countries to remain in them. Should they not have the option of escaping misery?

> What is going to keep people in their birth place, when they could earn orders of magnitude more in other countries?

There would be a new equilibrium. Poorer countries tend to be cheaper, so perhaps middle class first-worlders might move there (e.g. just like some Americans move to Mexico for retirement). Or perhaps the attachment to your local culture is strong enough.

But most important of all, why do we need to keep people in their birth place?