It looks like he's mostly concerned with flame wars and slurs, which makes sense since they destroy conversations driven by curiosity and turn them into bitter fights. That's not at all what is going on here.
The fourth comment down, and this is sorted by date not relevance, is almost isomorphic to this thread. I believe you didn't intend to start a "race war" (that's Dan's term, not mine), but the big subtext of HN's norms is being responsible not just for your intentions but for the effect your comment has on the thread.
It is not at all established that there are meaningful, coherent IQ differences between "races", and the process of hashing that out on this thread will be an attractive (and tedious) nuisance that will attract awful comments --- for instance, like one suggesting "brain size" differences between races are explanatory.
The OP pointed out a highly informative and important point and the majority of the negative responses to it have been from people who want to bash the American education system.
They are using cries of racism and bringing in irrelevant topics like IQ intentionally so that they can shut down legitimate conversation because they want to continue to bash the American education system.
It's not a highly informative point; it's a deeply contentious one that revolves around a narrow(ing) and disputed finding that is drastically smaller than the educational gap we're discussing.
