I should have caveated that statement with the fact that immigrants must be good people who sell labor to willing buyers and don't victimize innocents. I thought I made that clear by mentioning comparative advantage.

Unfortunately most poor Americans refuse to work, commit disability fraud and otherwise exploit the taxpayer, and commit disproportionate amounts of crime. (Far more than Indians - I've never felt unsafe in any slum here, unlike in the US). You don't get any comparative advantage from people who refuse to trade and merely take things from you.