What about Immigrants staying and benefiting their OWN countries economy?

Things will never get better in their original countries if everyone want's to go to a few very small parts of the world.

And things will eventually be undesirable in the places everyone is trying to immigrate to.

Whatever happened with staying in one place and making it better?

This sounds like a bullshit post-hoc rationalization for xenophobia. There's no valid reason to deny entry to any and all immigrants who are willing to work and have clean criminal records. Which side of an imaginary line someone is born on shouldn't determine whether they are doomed to poverty and oppression.

> Which side of an imaginary line someone is born on shouldn't determine whether they are doomed to poverty and oppression.

Getting rid of the line turns both sides into places of poverty and oppression.

Make the bad side of the line better.