I, as a proxy for the pro-immigration forces argue that exactly 1 question will determine how you stand on the immigration question. How much weight do we put on the lives of the immigrants?
If my life (friends/ingroup/neighbors/etc.) is the only one (group) that matters...then we keep them out. If we count the Quality of Life of an immigrant, though, as having even 1/10 the value of the QoL of a native...the utilitarian calculus is a slam dunk. We let them in...preferably barred from welfare for 2 generations.