I think people are wrong to oppose immigration while at the same time thinking that they can migrate, as they are sides of the same coin.

If you ask people if they think that they themselves should be denied the right to travel for extended periods and work abroad you will find very few who agree, even if they hold that view about people from abroad coming to work in their country.

Beyond that, I think that people are not so much morally wrong, but just plain stupid to oppose migration on principle. Populations rarely prosper without trade and trade does not prosper without migration.

As far as the 'preserving genetics' argument, that just isn't the way evolution works. The environment is always in flux and in general it is a bad idea to assume that a particular makeup should be kept static, as it is then doomed to be an evolutionary backwater while the growth is being done by those who are freely mixing.

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edit - @yetanotherphd, it isn't letting me reply directly to your post below at the moment, so I have posted my reply here:

It's like saying that we should cut all social services because everyone thinks they should be paying less tax.

It isn't like that at all. In that metaphor it is like asking both questions and pointing out that if you don't want tax then you can't have state services.

the most valuable trade is within Europe and East Asia, and yet East Asian immigration is relatively small.

That trade was built up over centuries and involved European empires all over the far east.

How can you explain the success of the very un-diverse Scandinavia?

The Vikings travelled most of the known world and shagged around a hell of a lot. Scandinavian DNA has genes from all over the place.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjourna...

http://www.spiegel.de/international/europe/dna-shows-genetic...

If you want to base your claim on some general theory, what about how plant and animal breeders maintain specific breeds instead of mixing them all together?

Go look up the genetic diseases of purebred dogs.

"Current genetic evidence refutes the theory of inbreeding for typological traits to achieve breed purity (18,19). Population genetics is the tool that exposes the fallacy of purebred dogs and, hopefully, it can also be the tool with which the canine species is revitalized. Population genetics is used to calculate gene frequencies, and the frequencies of alternative alleles within genes, both of which are integral to assessing the health of a species.

An individual canine’s genotype will dictate the production of specific structural and functional proteins, and in combination with environmental influences, result in individual phenotypes, or visible outcomes (1,20). If both parents supply the same allele for a particular gene, then the offspring is regarded as homozygous for a specific trait. If the alleles supplied by each parent are different, then the offspring is heterozygous for that trait. Heterozygosity is an important occurrence for species’ fortitude and survival (1). The Hardy-Weinberg Principle describes how a natural balance, in most species, maintains a high degree of genotypic heterozygosity in order to preserve genetic fitness and, hence, species’ health (2,4,18,19). High rates of homozygosity can occur in nature due to “bottleneck situations,” such as a limited gene pool in island populations, but in canines, homozygosity is deliberately accomplished by people trying to achieve specific breed standards. Many desired breed traits are recessive, rather than dominant, and require that both copies of the inherited alleles be the same for the trait to be expressed phenotypically. Individuals selected for consistent expression of alleles specific to desired physical traits results in offspring that are homozygous.

Breed purity and genotypic homozygosity is harmful to canine health because it requires inbreeding and results in an abnormally high occurrence of inherited diseases. Unfortunately, when breeders selectively “double up” on desired traits for physical conformation, they also double up on genes that can result in decreased fitness and increased disease."

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1950109/