What American shouldn't want to import more taxpayers? The income threshold over which a family is a net contributor to the government probably isn't much about $60K. So, importing just about anyone with a skill would lead to a lower tax burden for all. And, it would improve the lives of the lowest paid Americans by creating more demand for basic services (house cleaning, lawn mowing, etc.)
I understand the labor unions' reluctance to allow unskilled immigration, but they ought to press toward allowing more skilled people as it would increase the demand for their members' services. Interestingly, I think most unions are now in favor of legalizing illegal immigrants -- kicking out 10M people seems undoable, so they're best served by eliminating the illegal, un-unionizable underclass.