You do have a point. There is no difference. But you has misinterpreted the meaning of the word nationalism. It just means "national sentiment", and it's thanks to this sentiment that European nations have prospered culturally and economically.
Sorry, I don't think I am the one misinterpreting it. Nationalism is an appeal to denial of foreign territories, It is the full acceptance of permanent conflict. Appealling to one's lower instincts, as so richly illustrated in 1914 and 1939, as well as by the current trends, but ultimately and by necessity an utterly destructive instinct.
In the end, it is just tribal thinking with pretensions of greatness. Fine for living in ways that value pride and purpose over long term thinking. Entirely unworkable if one hopes to avoid calamity while living in a world with a population of billions.
The concept of borders is sacred because a territory belongs to a specific nation.
Sorry, Luca, but you are mistaken. There is no such thing as land ownership in any meaningful sense. It is only social convention by way of laws and customs that sustains the appearance of same. And keeping that delusion, understandable as it is, opens the way for more serious, often bloody and inhuman ones.
We all need land to live in and it is understandable that we want assurance of having it protected from interference of uncooperative people. But lying to ourselves about what can be assured is not a workable solution.
And each nations has a specific Volksgeist, and we European nations want to preserve this Volksgeist. Because there's a reason why Swedes are Nordic, Austrians are Alpine, and Italians are Mediterraneans. It's a natural process, involving genetics and climate. And we Europeans have preserved it for centuries. And we will keep doing it.
Every people is as detailed as we dare to look, being exposed and a part of many simultaneous cultural trends at any given time - and that is definitely a good thing, besides being unavoidable to boot.
Declaring nationalism as a real thing is ultimately an attempt at denying it out of political immediate convenience, attempting to decree some conception of "national" culture as truer than the many, often more vital and at least as legitimate alternatives.
It is not defensable from an ethical view, and destroys a whole lot of the basis of continued survival that humanity needs to deal with the challenges of this huge, unwise, uncooperative population. We won't conquer the challenges of dealing with others by declaring them less significant than those in the immediate vicinity according to static, arbitrary frontiers.