Earlier quoted context omitted.
> Anti-immigrant policies, are always conservative. I'm less familiar with this in the US, but in many other countries unions, which have traditionally been leftist-leaning organizations, are a major force against liberal immigration policies.
Good point, though I think that's for economic reasons and not for nationalistic reasons. Unions in the U.S., for example, long supported (and organized) immigrant workers who already were in the country and were early supporters of civil rights for blacks.
Even if you assume a one-dimensional political spectrum there's plenty of reasons for why someone might by for or against immigration for any number of reasons.
For simplicity's sake let's use the stereotypical US definitions of conservative and liberal, even then you can find plenty of reasons on both sides to be for and against immigration.
You could be conservative and be for it because you're a business owner and it implies cheap labor, or against it because you're also a xenophobe and just don't like people from other countries.
You could be for it as a liberal because you believe in some pan-nationalistic idea of humanity without borders, or against it because you think the influx of cheap labor will ultimately create a lower class within society which interferes with the project of a socialist state.
You mentioned Scotland as an example among the rise of the rise of right-wing ideals in Europe. I think it's entirely unrealistic to mention that in the same paragraph as nationalism leading to "massacres, and other oppression". If anything bad things might happen because Scotland is being denied national autonomy, just look at what's been happening in Ireland.
Sometimes people just want to do their own thing in their own little piece of the planet. I myself am from Iceland which has a long history of a nationalist movement that has nothing to do with any of that stuff. Sometimes people just want a bit of self-determinism without negatively impacting others. Ascribing that desire to left or right or conservative or liberal is a gross and inaccurate oversimplification.