I'll bet this will be locked due to the politics end of things in short order.
I would say that for the USA, I've heard and read that the entry visa for higher learning/genius immigrants, that a huge portion of great American minds in the last 50 years are immigrants, and become Americans due to that policy. I think that's great, and what makes/made America great, a beacon that welcomed all the best and brightest around the world, gave them the best environment in which to flourish, and rewarded them with all the better attributes that America had over their previous/birth nations.
That's all changed now, for the worse now IMO, and it isn't merely an American problem. Not much more than that could really be said here I think.