Well, it all depends on your experiences. In my experiences that I have seen, Mexicans can be pretty bad about the nationalistic thing.
For example, when the Trayvon Martin thing erupted, everyone in my class was against George Zimmerman, but when certain people found out he MIGHT have been PART Mexican, it was all alright then! He was just defending himself!
But of course, I am not saying all Mexicans are like this. In fact, I'm sure most aren't. But from what I have seen, it can get pretty bad.