We were all immigrants at one time. All that is true to one degree or another, but the simple fact remains that most Americans hate immigration because they hate immigrants. They hate the idea of sharing their country with Mexicans. Nobody had a problem when we took in droves of world-class scientists from the Eastern Bloc. Polish scientists won't kill your sons and rape your daughters.
Nobody wants to build a wall between America and Canada.
Canadians don't sell drugs. The country is going to hell in a handbasket. Whether or not we're doing it consciously, these are the assumptions we're working under. Our lives suck because an immigrant took our job, moved next door and bought a nice car. If they know the answer, then they don't pose a threat.