It's effectively a legally enshrined global class system.
While I don't think it's practical to just abolish the concept overnight, I do think it's ultimately the direction we should try and move in. The freedom of movement the EU offers is a step in this direction, and something I'd like to see more of.
I strongly disagree. The citizenship is a set of mutual rights and responsibilities between the citizen and their country, and a country should be under no obligation to allow people to live there that refuse to partake in their responsibilities. Should it be easier to immigrate? Probably. But the moment a country gives up the ability to govern their membership, they cease to be sovereign.
While I don't think it's practical to just abolish the concept overnight, I do think it's ultimately the direction we should try and move in. The freedom of movement the EU offers is a step in this direction, and something I'd like to see more of.