I won't bother to call "[citation needed]" on this since I'm sure there are biased analyses out there on both sides, but consider lifetime cost vs. working years remaining. Maybe we're economy-positive on an 18 year old unskilled laborer, even. But most pro-immigration policy changes involve a lot of older folk coming along with in the long run, and not everyone who comes and stays makes enough to be a net positive from a tax POV (not even considering the retirement/medicare time bomb).