Except those countries continue to decline and eventually become a global issue. India is on the cusp of a water crisis which is going to turn into a massive refugee crisis - how different would the situation and institutions be if the top 10% of the population hadn't been siphoned off?
Or would you rather condemn me to life in a corrupt, dangerous country even though I have everything it takes to build great things and make the lives of other humans better?
That moral argument against immigration, especially coming from an American, is DOA.
And from the perspective of the home countries, you're basically telling whoever happened to be born in a shithole that their only choice is to fix it themselves.