Real estate has been zero sum ever since we ran out of frontier. Employment is zero sum when immigrants (of any race) try to add a lot of labor supply and minimal demand to an economy that already had a severe job shortage.
Immigrants do not add "minimal demand", immigrants drive significant demand and expand communities, for example, bloomberg reporting that gas prices dropping may have a contributing factor that immigrants driving less this summer.
Lastly, our use of technology means that nothing is a zero sum game, we have created industries and growth through the use of various pulses of migrants and they are one of the core pieces of american success.
An migrant worker creates less demand than a native doing the same job, because they're trying to live austerely and remit as much of their income as they possibly can out of our economy and back to their family's. They aren't building out water and power homesteading our uninhabitable scrub, they're living ten to an apartment near the few jobs.