I don’t know all of the facts behind Jason Richwine’s resignation (or, perhaps, “resignation”) from the Heritage Foundation , so I’ll content myself simply to expressing agreement with Bryan Caplan’s take :
In a just world, no researcher would be fired for truthfully stating that some kinds of immigrants have low IQs .
In a just world, however, researchers would be fired for arguing that people with below-average IQs should be denied their basic human right to accept a job offer from any willing employer.
Despite their correlation, the two views are worlds apart . And despite popular opinion, it is the second opinion, not the first, that civilized society should shun.
I would add only – as a matter of emphasis – to Bryan’s take that a researcher who argues that immigration policy would be improved by screening out low-I.Q. immigrants is a researcher who doesn’t understand the principle of comparative advantage. (Bryan himself emphasizes this general point in one of the links that he supplies above.)
If you’ll pardon my vanity in this post that is already filled with too many “I”s, I made a closely related point last year in this essay for the Liberty Law blog  – an essay in which I argue that the economic case for allowing in more low-skilled immigrants is as strong as is the case for allowing in more high-skilled immigrants. My conclusion there:
Denizens of market economies prosper more the greater the mobility of capital to find its most remunerative (that is, most productive) uses. Ditto for resources. Ditto for consumer goods. And ditto for labor.
While we Americans should, by all means, make it much easier for the likes of foreign-born engineers, physicians, architects, and web-designers to immigrate to America, the same holds with equal force for immigrants whose skills are much fewer and far less sexy.