Not everyone ones: American citizens who compete with immigrants for jobs. Or H1B immigrant's compete for overall quota spots with other immigrants, so those lose.
I compete with H1-Bs every day. I don't have a problem competing with the ones who have green cards since their salary isn't artificially deflated. I do have a problem competing with an H1-B who is 40% of my salary and is stuck that way for 5+ years (even if an H1-B is hired at mostly market rate--the lack of raise in a hot sector drops their relative salary very quickly).