In the Western societies we have invented the fiction of races, sexes, ethnic groups, etc., having equal abilities, especially equal intelligence. This fiction is maintained by almost everybody (paradoxically, most fervently by the kind of folks who also strongly believe that neither intelligence nor IQ can be measured, making me wonder how these unmeasurable qualities can be considered equal).
This fiction has been invented because it has a very useful social function, especially in fairly individual-oriented societies: it encourages us to judge individuals as individuals and not as representatives of their race, sex, etc. It is a very useful fiction to maintain when hiring people, admitting them into schools, etc. Useful both for maintaining equal opportunity in society, and for the individuals in question.
It is, however, a fiction, in the sense of "an assumption of a possible thing as a fact irrespective of the question of its truth". We do not know it to be true. Any research in this matter is of necessity controversial, and often shows that it is not, in fact, true between some group A and group B, which then causes a scandal and accusations of sexism, racism, etc. It might well be true, too, for many particular values of A and B, but usually nobody really knows it. The Swedes of Finnish descent might well be equal in intelligence to Argentinians of Italian descent, but I find it highly unlikely that anybody has ever bothered to check.
The problem with this particular fiction is that nowadays a lot of people take it as The Truth - all available evidence to the contrary be damned - and everyone who doubts it as Nazis Who Are Already Warming Up The Ovens or, alternatively, Evil Sexists Who Plan To Keep Everyone Barefoot and Pregnant.
I think that it's a very good thing that every kind of social inequality between every group A and B is not immediately dismissed with "yeah, but A's are so much dumber, what do you expect?", but I find it unfortunate that in a lot of cases you can't even present the IQ or some other ability difference as one of the hypotheses, at least not in public and not without a major scandal.
There is one thing about all this that bothers me even more than the implications on the freedom of speech and the quality of research in social studies: do we, as a society, need this particular fiction in such a strong form at this point in history? This is not a rhetorical question - I really don't know. My gut feeling is "no, we don't", but I am nowhere near sure of it, and this might just be wishful thinking, because I find the implications of "yes, we do" rather unpleasant.
For all the sometimes-founded and sometimes-unfounded complaints of racism, sexism, etc., we are a rather egalitarian and individual-oriented society (the only exceptions being the result of either strong necessity or strong cultural tradition, and we are usually not comfortable even with those). Some of us dislike some group or other, but by and large even these people are usually capable of dealing with members of the disliked group on the individual basis in a civilized way. Most of the people who make hiring decisions are well aware that "group A is less intelligent that group B" does not usually mean "university X graduates from group A are less intelligent than university X graduates from group B". Etc., etc.
Will this all come unraveling if differences in abilities between various groups become acceptable to mention in public? I don't think so, but the thought is highly disturbing. I realize that the current orthodoxy is the result of the bad old times when people believed that all women, all blacks, etc. were incapable of holding a professional job, but haven't we moved far, far on since then?
Then again, maybe not.