It's possible for immigrants to both increase the health of the economy in the medium to long term and to cause localized economic pain in the short term. For those living paycheque to paycheque it's the short term that matters because they don't have the luxury to wait for the longer term effects to play out.

I say this kindly, you must have never worked a labor-intensive job and watched your friends(co-workers) get laid off for cheaper labor.