What exactly is it that americans feel for mexicans?

I am not mexican or american but I have always asked myself Why some americans don't like mexicans. Which are their feelings, their thoughts. I am neither agree nor disagree with illegal immigration but sometimes I feel sad for mexicans. They are everywhere but at the same time I have the feeling that they are always trying to hide from others. I like diversity and enjoy meet people with cultures different from mine. Please be respectful with your opinions. I am seriously curious.