Because the MSM,sleazy politicians and lobbyists tell us so.
And we don't question how much of our tax $$$ are spent on medical care, food stamps, free lunches, free education, rent assistance, child care assistance, etc., goes to subsidize the "cheap labor" costs of hiring illegals.
Businesses won't complain, because it's Joe and Jane Taxpayer that foot most of the bill for these illegal employees.
But I'm not a professional. Just a dreamer.