If you let everyone in all at once then the place becomes exactly where they are fleeing from then there is no point in moving. Trying it would be the end of society. We hasn't tried killing every third baby but it is probably not a good idea regardless.

When women couldn't vote most men couldn't either. Just landholders. Slavery was an improvement on killing entire populations and authoritarian monarchy were better than savages like Genghis Khan. Whatever trouble you have with recent history go back.. things were worse.

What would happen if Canada decided to do this. Couldn't China send in 15 million people who vote to join Canada.

Huge red flags.