The people who are most afraid of illegals are more often than not themselves upper-middle class. The idea of “illegal immigrants” is not really one of people moving into town to take your jobs. Abolition of unions and the atomization of the labor quashed that for the most part.

What people are obsessed with regarding migrants is the ever-present specter of Crime.

The idea being that these are very poor people who are entering your country, taking jobs that underpay, living in slums, and generally scraping just to get by. They’re definitely going to supplement their meager incomes by robbing the more fortunate. What’s more, when large numbers of migrants start living together, they form Migrant Gangs which are even more dangerous than individual migrants. They start working together (scary!) and planning things (oh no!) to change the place they’re living into one more reminiscent of their homeland. That means doing lots of drugs and playing mariachi music and putting up those spooky sugar skulls during Halloween and having Quinceaneras for their evil teenage daughters.

This is an existential threat to upwardly mobile suburbanites in their whites-only enclaves.