Of course, if immigrants are a net benefit to our economy, his desire is already fulfilled broadly speaking.
I've known quite a few legal immigrants in my life, and all of them were "productive" members of society. They came in the legal way of course, and were generally well educated when they arrived. The ones "sneaking in" rarely are of course. And I understand that some enter legally through amnesty or claims of religious and other difficulties where they lived. That group probably is a "drain" at least initially.
It's a bit weird, to me, that the act of being in the US without legal authorization is not in itself illegal.