(In the extreme case) the only people this serves to benefit are those who own the companies in question. It makes for an extremely unhealthy worker environment. Someone locally will always be undercut by someone external. This creates a race-to-the-bottom where the only people who benefit are the owners. Trickle down theory is bunk: rising tide for business owners does not necessarily uplift everyone else. It may be a net-positive for the world, but its decidedly a net-negative for those who are local.

H1-B visas/ immigration restrictions are there precisely for that: to prevent the loss of jobs that can be easily learnt/trained. Remember that we are talking of skills that are much more difficult to learn.

Definitely, and in those situation we should welcome them with open arms. I was assuming (perhaps erroneously) that he was speaking towards completely free and open talent-immigration, as in simply hiring an immigrant because they're cheaper and are are completely dependent on you for their visa.