And yet, at some point in history all those groups you cited were "stealing our jobs" and "dangerous individuals" whose culture is incompatible with "ours". See also, the myth of the model minority: https://www.learningforjustice.org/magazine/what-is-the-mode...
> Because within a generation they were impossible to tell apart.
I don't think that's a correct interpretation. I would rather say the conservative blamers found other scapegoats to blame, for example with other immigration waves