It is a hard problem, but there isn't enough evidence to link legal immigration to the shortages and unemployment that you have cited. It is as easy to say "there is some unemployment, so we should make life difficult for non-immigrant aliens, that'll fix it" as it is to say "the sun goes around the earth because we see it go across the sky." It is not clear if you can draw a causation between restrictive (or unfair policies, as it currently stands) immigration and improved employment rates. The debate will be better informed if you can cite studies that say fixing alien-worker policies fixes employment (to any extent). Here's a (partisan) starting point: https://www.uschamber.com/blog/guest-post-economic-impact-hi...