(1) If the knowledge does come out, the racists get to yell "I told you so," "Conspiracy of silence" etc. Then the IQ difference gets magnified 1000x in the public imagination.

I think we are seeing that among the for now (fortunately) small group of relatively intelligent unconformist people who change their opinion on this subject once looking at the data.

It biases them towards unduly sympathetic judgements of everyone else who happens to hold the same opinion.

"Oh that guy is just a bit rough around the edges, he's just ranting in that post. I kind of understand him, its so hard to keep seeing the same lies and falsehoods behind repeated over and over and over again."

or

"I'm mean sure he's wrong on that, but we can't be picky in choosing allies in our fight for truth when our opposition has the full weight of the state on their side. "

or eventually

"Yes the guy is a douche and bigot but if we are ever to stop wasting 4% of our GDP on policies based on this falsehood we need to be political realists and just work with them."

Leaking unconfromist, driven, principled (as in truth seeking even when it costs them status) intelligent people to otherwise unworthy causes? This may prove to be dangerous in the long term.

One can't overestimate the propaganda value of calling out a well intentioned lie out as a lie and then proving that it actually is, you know, a lie. Our biases make us very vulnerable to be overly suspicious of someone who has been shown to be a liar. This is doubly true of our tendency to question their motives.