For the US and Canada this is in a way even weirder: the vast majority of the population there can trace back their own roots to immigrants, I find it hard to imagine if you know your own history to that degree that you would object to other immigrants.

For Europe: not all that long ago many here were refugees, on the run for the Nazis or during other wars. Immigration and refugees are a sign that the world isn't working well, a symptom, not a cause and you can't cure symptoms.