in my small bubble of experience those people come in, work their butts off and scrape by. yeah some of them waste public resources but many of them just survive on scraps bc they're coming from poverty to slightly better poverty.
i could be wrong, but the drug/sex smuggling is the only problem and that hides in the fog of "regular" migration.
look the other way when 100 people get smuggled in and the 2 or 3 with ill intent get through easier.
make it simple for honest people to check in, get searched, document themselves, register for taxes, and suddenly the hard core criminal element can't hide in the flock. every effort made to keep the borders wide open, call immigration control racist, or shout about non-sequitir h1b system problems is to hide the rat lines of in-plain-sight criminality.
but just a guess i don't have direct experience.