Immigration is good for economic causes but when too much immigrants settled down and threatening the demographic change, that's where it cross the line for most people I think.The Natives will feel threatened and thus rise the nationalism. Most countries and states today was named or owned after the dominant controlling community's identity. One need to always remember that. If you don't assimilate with these group of circles you're likely to not feel welcomed or accepted even in your 6th, 7th generation immigrant. As the saying goes Once an immigrant always an Immigrant.
There's serious Brain Drain problems among 3rd world countries. Sure, one might argue the current world order is deliberately designed that way to keep these countries poor and lure talented peoples coming to 1st World to boost their economies but still, always keep a connection to your homeland so that you can return one day and help it to rebuild instead permanently settling in foreign lands
If you're desdecants of immigrants who neither feel accepted in the country your living nor feels home in your homeland. Then congrats.