These are the brightest minds on the planet. We should do whatever we can to make them OURS.
Of course we need to minimize intellectual theft... but this probably only involves a minority... and we should beef up our efforts to curtail the worst cases.
Instead, we should encourage and enable them to stay and contribute.
When I did grad work at Berkeley the most brilliant students I met were Iranians... ALL OF WHOM DETESTED THE ISLAMIC REGIME.