It isn't. Every serious study shows we need immigrant labor to even survive.

America's population pyramid is completely upside-down. When it comes to our citizens, way too many of them are retired. There just aren't enough younger citizens to support the needs of the retiring Boomers. The labor pool isn't there. Every crazy old person complains their Guatemalan nurse is stealing their earrings, but she usually isn't, and they need that nurse.

This exactly why Republicans have spent the last few decades shouting anti-immigrant rhetoric to the base while doing little-to-nothing to stem the flow of immigration. Because that would cause many of their their donors' industries to collapse. So they lie to their base, and then keep the economy running.