That does sound like bad news for exploiters, but it sounds like a good thing for people who actually want people to be better off. If open borders means people come, work for cheap, improve their homelands, and eventually stop coming, that sounds like a win-win to me. Are you sure some of the open borders folks aren't thinking like that?

If rich countries' sustanibility depends on poor countries staying poor, it creates a huge incentive for the rich countries to destablize the poor countries and keep them poor.

Just like the US once destablized its southern neighbors to keep them exporting cheap fruits, if the only thing that keeps the US's pension system from exploding is cheap workers from the neighbors, it'd want them to keep exporting cheap labor.

Of course one might argue rich countries will do that anyway so it's not a concern. It's just icing on a poisoned cake.

The issue here is that nowhere is the wellbeing of the low income natives considered.