The US economy was booming before the ZIRP began though, and that was on the strength of the technology industry. Immigration does fix two particular problems

The US economy was booming before the ZIRP began though, and that was on the strength of the technology industry. Immigration does fix two particular problems though, especially targeted immigration of skilled workers rather than refugees: 1) It balances an aging, shrinking population which usually stifles innovation and depresses wages (both of which are happening in Japan right now). 2. It increases the talent density of industries. Talented people exist in every country and culture in the world. Attracting them to your country with a wage higher than their home wage is a good way to snowball a competitive industry (because these talented people make things successful leading to more opportunities for more talented people).