I love the ironic ignorance of history, linguistics, and anthropology that leads to articles like this. And I love the totally ironic error in the sub-headline:
The inability to speak a host country’s language ... is a very reasonable requirement of any immigrant.
I guess the Normans don't belong in England. The Saxons came after the Angles, and THEY replaced the Celts, who were themselves cultural and linguistic invaders. None of them spoke the "native" languages.
But what is more ironic is that the author claims that we need to all speak one language so that we don't have "dangerous divisions". This is a totally unsubstantiated claim; lots of countries do just fine with minority populations that speak different languages; but then the author goes and cites CANADA as an example of a country that requires a language test to get in. Um... maybe someone should tell him that we don't all speak the same language in Canada? Yeesh. I guess we're dangerously unstable? Oh wait... nope, it's just a few crackpots that occasionally cause the odd ruckus about Quebec, while meanwhile separatist sentiment waxes and wanes. Oh wait, didn't England have a problem of this sort? Like, hm, Ireland? I'm pretty sure they speak English there.
I addressed some of the points about immigrants learning new languages in my previous post on this topic. To sum it up, I don't think it makes sense to force immigrants to learn the language when we don't force natives to learn the language. Research has shown (and your own intuition should also show this) that the children of immigrants assimilate quite quickly and within a couple generations they are indistinguishable from the natives. This is most true when it comes to language, as children learn languages really really easily.
What this all amounts to is that language is used as a proxy for racism and xenophobia. You can't shut the door on immigrants, you can't single out all the Muslims or Indians who want to move to England, but maybe you can raise the bar high enough that it's impractical for those people to move there.
As an aside, Joshua Gans wrote about his taking of the English test for moving to Canada. Frankly it's quite absurd that an economics professor from Australia, who has published books in English, is made to take a test to prove that he speaks the language. Surely this is something that would be immediately apparent from a simple 15-minute interview? Testing native speakers is a waste of time and money, and testing other immigrants is xenophobia and racism.