In some places the zeal to prevent illegal immigration spills over onto the Mexican community of born or naturalized citizenry. For example...in Sheriff Joe Arpaio's Maricopa County, the policy was to pull over drivers who appeared "hispanic"...the majority of whom were born in the USA.
That's one reason which, critics claim, is based on another more general reason...namely the inherent racism towards "hispanics". There's no shortage of examples of white racism toward "hispanics" either in history or the news.
I get what they're saying and I agree to some extent. Arpaio did conduct business in a racist way. A lot of white folks in the Southwest where I live act surprised and butt-hurt that Mexicans live in what used to be Mexico until the USA took it by force. The critics have some points.
But Open Borders? NO WAY. That's a naive and dangerous idea.