Thank you for coming up with the first answer to my question. These studies are surely valid and merit recognition in their own right. They focus on the right mix of issues at stake. However, while I’d like to include all three studies as references to my paper, they do not answer my question.

Indeed, some immigrant groups seem to adapt well, while others become a social and financial burden for the hosts. This is very much an issue of finding synergy and fit between the two populations – hosts and newcomers. It is also about the predominant ethos of a given institutional environment. Consider that corporations who hire a diverse workforce still carry out screening of the competence and aptness of each candidate. Same with universities who enrol ethnic students: those who are selected are unlikely to find themselves in conflict situations with their native counterparts.

So, I wanted to know about the case of extreme diversity; by this I mean the widest imaginable distance in observed traits between immigrant and original groups. In the old days, it would have been safe for us to speak about fundamental difference in ‘races’ but today we just might talk about wide ethnic differences. We may not need to go as far as Richwine (2009), who proposed admitting immigrants based on their IQ levels (and who four years later lost his job because of some journalists from the ‘liberal’ camp complained about his findings); we just need to accept that some groups are too far off in terms of cognitive inability and/or cultural incompatibility. To use your case, Romanians and Canadians are both White, European and Christian in origin. Casually observed, ethnic Romanians who move abroad are often educated, and speak both English and French. They are furthermore relatively well-known for being rather adaptable to life in the host society. So instead I would welcome similar cases with uneducated Muslim immigrants from conflict/upheaval ridden countries in Africa or Southwest Asia.

You might look to studies done in Canada, however, for some answers, given that Canada's immigrant population is "extremely diverse," with a high percentage representation from groups other than those who may be considered White. This may provide a starting point (although the particular link offers a policy overview, there is some discussion of effects of policy): https://www.migrationpolicy.org/article/canadas-immigration-policy-focus-human-capital

Thank you for the link. This article is informative and, yes, the Canadian experience surely is interesting. So, I definitely agree that diversity also can have benefits, as long as it can be controlled. Now, assuming that the optimal diversity is somewhere between the low and high ends of any scale, the issue is then with what kind of policy this optimum is reached. Before checking this link, I would have said that any possible benefits are contributed to the relatively strict immigration policy implemented (i.e. movement towards an optimum level), and that other developed countries with strong imported diversity, such as Sweden or France, fare worse exactly because of their more liberal approach to immigration (i.e. movement away from this optimum). Let us now examine the evidence.

According to this article “…the goal of the immigration system is to encourage youthful, bilingual, high-skill immigration in order to build human capital within Canada's aging labor force. In order to attract the right type of migrants, Canada has set in place certain education and skills provisions that work to advantage potential migrants who have work experience, higher education, and English or French language abilities.” Indeed, in Canada the immigration policy can be considered selective. And the article laments “…a sharp division between immigration policy intent and outcomes”. So diversity was not that beneficial after all.

While immigration policy in Canada has changed, a relatively controlled approach has remained in place. As “…Canada has sought to target its immigration benefits toward potential immigrants with characteristics that coincide with Canada's evolving needs and interests”, I do not see how this can be presented as evidence pro benefits of extreme diversity. And: “Immigrants in Canada tend to be highly educated, in part reflecting the fact that today the majority of those who come to the country do so through economic-class streams”. (Compared to Europe, the longer distance from home countries of prospective refugees inevitably matters here too.) Furthermore: “…the labor force participation rates of the foreign born converge with those of the Canadian-born population”. The article also notes how immigrants are poorer than Canadians (but unfortunately, it does not compare crime rates between the two populations.) The article concludes with worries about “… social mobility opportunities that exist for immigrants, and the Canadian economy's ability to absorb foreign-born workers”. So, my initial assumption stands: even Canada’s Human Capital based approach is detrimental to some degree.

you can read about model bicultural identiity integration from Martínez, V., & Haritatos, J. (2005) to see how the diversity bring harmony and conflict.

@ Dr. Sarifin:

Thanks for the reference, quite right: diversity brings both harmony and conflict. I never disputed that (see my previous comments).

@ Dr. Joumaa:

Again, see my previous comments: some ethnicities are adaptable, others are not. So, for example, ethnic Romanians (with the possible exception of Romanian gypsies) belong to the former category, whereas many other ethnicities (hailing from farther afield) do not. Similarity may not be the key issue but it helps in generating the necessary trust between the two groups (in Putman’s sense). And my intentions are not to defend anything; it is more that I need to be sure that my academic writing is objective enough. (I am grateful for your remark as it made me rethink my position – I think we can both be right on this, as long as we mean same concepts.)

Thanks also for the reference. However, it does not really provide evidence for my question, because it is a prescriptive report about multicultural services needed for accommodating this diversity. Much of the text is about what is ‘needed’ in a given place. So it is already assumed that multiculturalism/diversity always is necessary. The authors miss the essential point: if immigrants cannot survive without such massive support systems, then we cannot really claim that these places are success stories in this respect. (In a historical perspective, Europeans who immigrated to America where seen as successes exactly because they could create their own success.) Besides, not sure what is so ‘extreme’ about the ‘extreme diversity’ reported here.

@ all four who responded so far: this documentation will comprise appendix info for my paper; in the name of ethical issues, I would like to ask each of you: is it alright to include your names in my documentation, or would you rather be anonymized (completely/partially), and if latter, exactly how?

In any set of circumstances, there will be pros and cons and gray areas. Immigration is a complex problem to be sure, compounded by issues such as climate change, civil war, widespread violence, and other issues that cause people to make the hard to decision to uproot themselves and move elsewhere. Some sense of ethics and morality typically is embedded within any policy decision (the words behind the words); I would argue that Canada's goal of finding the "right kind" of immigrant conveys a subtle racism and classism, but Canada has also been relatively generous (moreso than the US, anyway) with its openness recently toward refugees--an indication of the moral and ethical concerns which also affect immigration policy. My question: who has the right to "control" immigration? In Canada or the US, the easy answer is the government and policy-makers––-but what about the Indigenous peoples who occupied those lands long before the European invasion who are largely disenfranchised from the decision making? What are their rights? (Admittedly I am speaking from a North American perspective, but I think the question may apply anywhere there are oppressed ethnic groups). They are now "controlled" by those in power, and have long been abused by those very forces. I worry that seeking to prove negative benefit provides fodder for authoritarian, fascist factions which have been gaining influence in governments world-wide. My preference would be to find ways to make life more equitable for all human beings--those living in the lands onto which they were born as well as those who have emigrated to a new location for whatever reason. If an investigation's goal is to seek negative outcomes, I would hope that research would then be used to effect positive change to benefit those harmed by the policies.

Arthur Schlesinger addressed many of the issues surrounding diversity and multiculturalism. His book, written in 1998, foretold many of the problems we now see with modern multiculturalism. His work is such, that I found it still useful in 2019 for some research I am doing for Penn State U:

"the ethnicity rage in general and Afrocentricity in particular not only divert attention from the real needs but exacerbate the problems" (Schlesinger, 1998, p. 106).

Schlesinger, Arthur M. Jr. 1998. The Disuniting of America. Reflections on a Multicultural Society. W. W. Norton & Company.

@ Dr. Bradley:

So the benefits of immigration related decisions can be of many kinds, either economic or multidimensional. The host society obviously have to decide about them, preferably through democratic process, at a national (and local) level. Otherwise, European Americans might share the fate of Indigenous peoples and Western Europeans will also be minorities in their own countries (i.e. Great Replacement). And it is not only about rights; there are obligations as well. Anyway, I was interested in evidence, not ideology.

@ Dr. Caplan:

Thanks, I have to look it up. What you say strengthens my initial assumptions.