I don’t understand why there is so much angst about the southern border and not as much about the northern one

Having lived around Mexicans most of my life, I think it's because they're willing to work at physically demanding jobs that many Americans don't. Also, you become a friend with a Mexican, it is "mi casa es tu casa" translated "my house is your house". They love to share and they're very hospitable. Some of my closest friends were and are Mexican.