Who should decide what topics are off-limits?

Noah Carl, a young British social scientist, stands accused of peddling "racist pseudoscience." And as I discovered, even asking whether the accusation is true invites the same sort of unwelcome attention.

Hundreds of academics have signed an open letter about Carl's work, calling on his employers to publicly disassociate themselves from his research and investigate his appointment to a Cambridge University fellowship. The letter, released earlier this month, cited Carl's attendance at a much-criticized conference on intelligence in London, but it didn't go into detail about his research.

Carl's published papers address sensitive subjects such as Islamist terrorism and immigration. More provocatively still, he has argued in favor of researching race and IQ. But since the open letter didn't cite specifics, defenders of Carl's academic freedom could only guess at what had provoked it.

That is not, critics of the open letter said, how academia should work. Jonathan Haidt, a research psychologist at New York University, told me, "Academic norms are very clear, which is that you're supposed to rebut arguments; you don't use guilt-by-association."

I wrote to signatories asking for more-specific critiques. Many responded thoughtfully. But the sheer number forced me to send group emails, which turned lively when a member of the Cambridge English faculty promptly warned the others that Wikipedia placed me on the political right.

I protested that while the description was accurate, I was simply trying to understand their case. In a flurry of replies, she said that "It would be horrible to respond in good faith and then find out you were mugged," delved into a decade-old blog argument I'd had about Obamacare, and shared correspondence from someone else condemning the "racist banality" of my writing. Further protest from me was obviously useless; my political inclinations were proof enough of my ill intention.

Investigating links between race, IQ and genes has long been anathema; Carl's case suggests that it is now anathema even to ask whether those investigations should be forbidden. And I seemed to be proving that it is anathema to ask whether it should be anathema to ask ...

All somewhat ironic, considering that I already leaned toward believing that research into race and IQ should be off-limits. And that the defenders of Carl's academic freedom were the ones who had best made that case.

While some signatories provided detailed methodological criticism, research psychologist Lee Jussim argues that his critics are using excessively high standards that wouldn't apply if he had come to different conclusions. But I asked Jussim to respond to a deeper critique I've long been worried about, one concerning Carl's most controversial paper.

There's a history, I said, of scientists finding whatever they expect, from scientists insisting that humans had 48 chromosomes, even as their experiments kept showing 46, to the eugenics that fueled the Holocaust. One of Jussim's own papers shows that left-leaning social psychologists have long been inadvertently biasing their research toward answers the left finds congenial.

Given flawed scientists and imperfect scientific methods, and given the fraught history of Western racism, isn't the likelihood of getting it wrong just too high? And the potential cost of those particular errors simply too catastrophic to risk? All societies place some questions out of bounds because they're too toxic; we don't debate whether child molestation or spousal murder are acceptable.

Without hesitation, Jussim agreed. Carl wasn't endorsing a link between race and IQ, Jussim pointed out, just starting a discussion about whether we should study it. "If we had that discussion" he said, "I would personally advocate for a moratorium for all the reasons you just described."

"The question is not 'Should we have third rails in science?'" Haidt said. "That's a valid argument. But the question now is 'Should we randomly shoot anyone who gets within an unspecified distance of a third rail?'"

My own experience illustrates why the answer to that second question should be "no".

The Cambridge English professor wasn't the only one who seemed to assume my reflexive agreement with Carl, making reasoned argument fruitless. In fact, I've long suspected the impossibility of doing such research with what historian and signatory Daniel Cleary calls an adequate "duty of care." But I wasn't better persuaded by implicit accusations of bad faith. Instead my conviction was bolstered by people like Jussim and Cleary, who argued methods rather than character.

In fairness, however, I did emerge with two prior beliefs basically confirmed: first, that research into race and IQ should stay off limits, but, second, that those limits are better established by debate than denunciation.

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Megan McArdle is a Washington Post columnist who writes on economics, business and public policy. She is the author of "The Up Side of Down." McArdle previously wrote for Newsweek-the Daily Beast, Bloomberg View,the Atlantic and the Economist.