Smart and motivated people is in limited supply, so nations would complete for them. No graduate students, or postdocs, have ever got rich from their stipends while perform research in the US. Otherwise more American youth would want to work in university laboratories instead of the Wall Street. China is doing everything to bring their best talents home, because they also have invested a lot of resources on them. It still a sound investment for the US to attract the best talents from anywhere in the world to be educated and perform research here. If just the top 10% of these people decide to stay in this country, then everyone benefits from that. Furthermore, it is easier to find and recruit the best talents and for them want to stay, if they are educated here...most be the koolaid you find in the cafeteria.