The author suggests that just slowing down research into risky technologies in other countries would be worthwhile:
The lack of acceleration of science following the high skill immigration shock to the US is not necessarily bad news: it may also imply that future shocks won’t accelerate risky technologies, that research funding is a more fundamental constraint, or that other sectors of the economy are better at absorbing high skill immigrants.
Further emigration likely decelerated progress for potentially risky technologies in the former USSR, which is a net reduction of risk: there is less incentive for the US government to engage in an arms race if there is no one to race.
The author suggests that just slowing down research into risky technologies in other countries would be worthwhile: