I personally would put that limit a lot lower, more like 2 years or however long it could reasonably take to process an asylum request if you subscribe to this concept at all (which I really don't, I'm all for completely open borders or disbanding them altogether, it's the only way citizens of various countries get to vote with their feet).
>it's the only way citizens of various countries get to vote with their feet
You're not supposed to "vote with your feet". That's called "fleeing" and those who do it are "cowards". You're supposed to fight and make your country better, including bringing down an oppresive regime etc. For ages, even women and children have fought for freedom and for making the world a better place, including risking their lives. Rosa Parks, for but one example, didn't "vote with their feet".
As for "completely open borders" that either happens when all the earth is a united country (where everybody can vote for the general leadership), or is just crazy talk when there are sovereign countries that are more and less powerful.
If you call someone fleeing an oppressive regime a coward then you're more than likely not currently living in one and have even more likely never lived under one. Let me give you a history lesson, on the off chance that you'll prove me wrong. When you live under an oppressive regime the sum of the power stacked against the few that would do something about it is such that they have three choices: rise up and be cut down, shut up and comply or flee. If you feel like judging any of those that either comply or flee as being either cowards or worse then you forget that ordinary people typically just want to get on with their lives without interference from the authorities. Not everybody is in a position to risk all for an improved status quo, for instance. Those that do are to be commended, those that don't are not to be despised. That's all that I can impart to you from my (short) time of voluntary stay behind what was then called the Iron Curtain, but it is a lesson that stayed with me.
As for the crazy talk, I can definitely imagine a world where there are no border controls but where countries are still sovereign to greater or lesser extent. There are vast regions in the world where we have exactly that situation right now, I don't see why it couldn't apply to the rest of it. The current leader of North Korea might agree with you that this is crazy talk, but then again, that's exactly my opinion of him.
