Illegal vs. legal... it doesn't matter anymore to the right wingers. They used to really hang on this idea that illegal was this horrible thing that made all the difference. "I'm not against legal immigration, just illegal immigration" used to be the line. That was pretense.
The core of the panic is that outsiders are threatening the American way of life, and that multicultural Democrats are encouraging a cultural shift by bringing outsiders. This can be blamed for all kinds of problems, from rising prices, to unemployment, crime, poor schools, even traffic.
Xenophobia is what this is, combined with a heavy dose of confirmation bias. They're scared of outsiders, and they perceive the negative effects of outsiders in every traffic delay and purchase, whether related or not.