Governments might try to prevent people from leaving but at that point they are only buying time.
That's not the problem with citizenship. The problem is, other countries will refuse to let you in, or make your life miserable and you won't have the same rights as citizens.
Of course. Why would they let you just show up? You have to offer your target state something they value, it will depend on the state whether it's cheap manual labour or learned skills, or something else, or in some cases both. Once you can do that, proceed to my second point.
I am a citizen of a wealthy country, but I didn't earn this privilege, I got it by birth, and that gives me more rights than a lot of poor people working here much harder than I do.
Oh, go ahead, eliminate citizenship. Then states will instead privilege their current residents, a rose by any other name.
Countries/states/provinces/regions/cities are organizations of people, by definition people living in the geographical area (minor modern aberrations like small amounts of nonresident citizens notwithstanding). I'm really not sure how you imagine doing away with a notion of citizenship will convince a group of people to allow "others" into "their" group if the others don't offer the group something it values. This isn't evil statesmanship, it's basic human psychology.
I'm really not sure how you imagine doing away with a notion of citizenship will convince a group of people to allow "others" into "their" group if the others don't offer the group something it values.
That's a fair point and I don't know what would happen if we eliminate citizenship. It might be replaced by something just as bad. I'm just pointing out why I dislike the concept, how it is similar to nobility.
That's not the problem with citizenship. The problem is, other countries will refuse to let you in, or make your life miserable and you won't have the same rights as citizens.