@Ailchu,
I edited my response to you so much that I am re-posting it here. I also added some data.
I think the Dutch and Scandinavians are far closer to each other than either is to Italians. Italians are, of course, a bit heterogeneous, so let's talk about, say, Scandinavians versus Central (Lazio) to Southern Italians. I think they are very different in terms of lots of traits, both physical and psychological.
Let's start with the trivial: physical appearance. On "average", they look very different.
Then look at mental and physical health characteristics. All ethnic groups have members who carry genes for every kind of mental and physical illness, but the "prevalence" by ethnic group varies by specific type. Don't hold me to specifics, because I'm going by memory, but I think Scandinavians have a higher tendency to clinical depression. They also have higher statistics for suicide. Same for cancer of the colon and for alcoholism. The latter is at least true for the British Isles and the Netherlands, and perhaps Norway. Certainly it's true for Finland. I think with Italians it may be anxiety and bipolar disorders, and things like high blood pressure. In terms of violence, it's much less often suicide, but more often "crimes of passion". Which specific traits don't matter. Every group has good ones and bad ones. The point is that they differ.
Then there are what you might call social/psychological traits. Imo there is a large difference in terms of introversion/extroversion. I remember that years ago a Finn posted a picture on either this site or another one of Finns waiting for a bus. It made a HUGE impression on me. There were perhaps 5 or 7 people as I remember it. Not ONE was talking to the others; in fact there was more than five feet between each of them. You would NEVER see that in Italy. People would start talking, complaining perhaps about the bus or the weather or talking about the news, perhaps even arguing, but at least engaging. Now, I'm sure the Finns and other Scandinavians like it that way and that's fine, but I could never live in a country like that.
I could go on and on, but you must know what I'm talking about.
Now, if Italians want to marry Scandinavians and vice versa and so the differences disappear, or, as here, all these Irish and Italian people intermarry and so the specific "ethnic" traits get diluted, I'm not going to tell them they shouldn't do it, but I didn't do it myself. It didn't feel "comfortable". I didn't feel as if I fit with their families or they with mine. Now, for Italian Americans it's different. It's different for my children, but as they get older even they seem to be gravitating toward possible "mates" who are at least partially Italian. It becomes clear as they interact with the partner's family and how the partner lives and inter-reacts with others that the differences are large.
Whether we like it or not marriages or partnerships, or whatever you want to call them, between people of similar backgrounds are less stressful, and less often end in divorce. Now, those are averages, statistics, there are always individual cases where it makes no difference. One of my closest friends, an Irish guy from graduate school, married an Italian girl, and honestly, they have one of the most perfect relationships I've ever seen. We're talking about relative risks here. Of course, he joined HER world much more than she did his, partly perhaps because he was an only child, and son of only children. I have to say this if I'm going to be honest. Anecdotally, when the wife is Italian and the husband is something else, especially, say, Jewish, the marriages seem to have fewer problems than when the husband is Italian and the wife is, say, Irish or German. The Italian husband, Jewish wife also seems to work better. Greek/Italian marriages also seem to really work out, but the Greeks are much less likely to "marry out" than Italians. That may partly be a religious thing. Both Italians and the Irish and a lot of the Germans are Roman Catholics, and that used to really matter, and still matters to some extent today, while Greeks are Orthodox. Like Jews, if they do intermarry they usually demand conversion of the non Orthodox partner. That would have been fine with me even years ago when I was a religious girl. I like Greeks, get on with them, understand their families, and even back then, I was taught in theology class that the differences between Roman Catholicism and Orthodoxy were more political and technical than spiritual, and if, for example, I were in some place in the Midwest where there was no R.C. church, to go to an Orthodox Greek one for Sunday services.
Also, if you're implying that there might be a time in Europe where there would be no actual "Italians", or Spaniards, or Germans or Irish, i.e. just an intermarried mass, it might be inevitable, but no, I personally wouldn't want that. To be clear, it's nothing to do with superiority or inferiority. I love my people, our history, our accomplishments, and I even find some of our many faults acceptable or even in some cases endearing. So, no, I don't want them to disappear.
Even in countries like the U.S., there is less intermarriage than Europeans sometimes imagine, at least across "racial" lines. I've posted recent data on other threads showing that 90% of "white" Americans marry white Americans. It's just the way it is, and I think it will stay that way for a long time, regardless of what "Hollywood" would prefer. There are also still Irish or mostly Irish descent people who would prefer their children marry people of Irish descent. It's just the way it is.
I see it happening in my own community, which is white and Christian, and has been for decades. In recent years a lot of Chinese people are moving in, and while no one is broadcasting it, people are moving further out on the island. It's not that they're not considered highly intelligent, hardworking, law abiding, all those things, but the "culture" is very different. It happened in parts of Queens, a borough of New York City. Whole areas like Flushing used to be Jewish, Italian, Irish. It is now completely, and I mean completely East Asian. I don't think a young European descent family would feel comfortable buying a house there nowadays. These old established communities are very sports oriented, church oriented, civic association oriented, summer life revolving around tennis and swimming and golf at country clubs or local community pool and tennis clubs. The School Association is very important, with parents being very involved in being class mothers, all that stuff. That's just not part of the culture of a lot of these very nice East Asian people, so there are some stresses.
I have some personal experience of the Italian/Swiss German marital mix. My first cousin married a Swiss German. He's a very nice guy, and she seems happy enough, but to my eyes she has totally changed her "personality" or traits, as much as one can do fighting genetics, and the way they "live", if you know what I mean, is completely Swiss German. I would NEVER, EVER, have done that. Of course, I may be biased here, to be honest, because Switzerland was the only place in my whole life where I was ever treated badly, indeed harassed, because I'm Italian. I was a teenager, and yet I've never been back. If my cousin wants to see me she can come to Italy when I'm there every year. I hold REALLY, REALLY intense grudges, and never forget insults.
Some data. I got some of it wrong. Bi-polar and schizophrenia rates seem to be the same for every country. The major differences are in alcohol/drug disorders, depression, and anxiety. I knew Italy would be lower in the alcohol and drug disorders, but I thought it might be higher in the anxiety disorders, instead a country like the Netherlands has more of it. Go figure. I absolutely don't get the low anxiety in some eastern countries. Maybe they consider it normal and don't get treated for it.