It takes a lot before a person becomes a serious professional or a scientist - you need a bright and highly motivated youngster, willing to put in the effort over many years. You need luck - meaning, everything must go well. You need a very significant investment of money and resources.

As an illustration, a couple of days ago I saw a photo of Elon Musk in a room, with a crowd of TWTR employees - apparently, people who are staying. The large majority looked like they may be Indian or Chinese.

To turn them away by the thousand is… bigly counterproductive.