I read on the Wikipedia page on Walter Pitts that Norbert Wiener broke off relations with Walter Pitts, which "sent Walter Pitts into 'cognitive suicide'".
Why did Norbert Wiener break off relations with Walter Pitts? The Wikipedia page argues that:
Wiener suddenly turned against McCulloch, on account of his wife Margaret Wiener who hated McCulloch, and broke off relations with anyone connected to him including Pitts.
Was it the only reason and if so why did Margaret Wiener hated McCulloch?
Another view of the split comes from the John Hopkins University document Walter Pitts (Smalheiser, 2000), it seemed to be a compounded effect of Pitts and his friends McCulloch, Selfridge and Lettvin's activities.
Possibly starting with Wiener's concern about the progress Pitts was making with his PhD thesis
Wiener was worried about Pitts making adequate progress on his Ph.D. thesis (concerning the state functions of neuronal networks arbitrarily connected in two and three dimensions), and tried to separate him from the distracting and corrupting influence of his pals Lettvin and Selfridge, who were engaged in endless scientific and money-making schemes.
Wiener almost broke ties when Pitts was supposed to return some documents back to him:
One comedy of errors nearly led to Wiener rupturing his connections with Pitts and the others. Pitts had been given a copy of a manuscript of Wiener’s to return to him, but he had checked it in the cloakroom in Grand Central Station in New York and had given the claim check to Jerry Lettvin—who, after a fortnight, gave it to Oliver Selfridge to pick up. Selfridge failed to find the case at the checkroom. Several months later, when Lettvin was next in New York, he inquired about the case, and eventually found that it had been sent to Chicago as unclaimed property, requiring several more months to be recovered.
But, it appears that the final straw was
Norbert Wiener made a sudden, irrevocable break with the others over an alleged slander involving one of the members of his family.
It appears that Norbet Wiener had simply had enough, a decision that no doubt was influenced by his wife (and possibly other family members and other friend).
Amanda Gefter's recent article in Nautilus takes a very unambiguous position on the question:
There was just one person who wasn’t happy about the reunion: Wiener’s wife. Margaret Wiener was, by all accounts, a controlling, conservative prude— and she despised McCulloch’s influence on her husband. McCulloch hosted wild get-togethers at his family farm in Old Lyme, Connecticut, where ideas roamed free and everyone went skinny-dipping. It had been one thing when McCulloch was in Chicago, but now he was coming to Cambridge and Margaret wouldn’t have it. And so she invented a story. She sat Wiener down and informed him that when their daughter, Barbara, had stayed at McCulloch’s house in Chicago, several of “his boys” had seduced her. Wiener immediately sent an angry telegram to Wiesner: “Please inform [Pitts and Lettvin] that all connection between me and your projects is permanently abolished. They are your problem. Wiener.” He never spoke to Pitts again.
Gefter references Conway & Siegelman's 2006 Dark Hero of the Information Age, a biography of Norbert Wiener. It's a great pity that Pitts' life isn't better documented, because he was, from any point of view, a fascinating genius, as was recognized at the time.
I make this answer tentatively since I cannot find the document, an autobiographical chapter by Lettvin I read some years ago which discussed among other things this situation. Lettvin had a whole book available online, but searching I can't find it.
Basically, Lettvin claimed that Pitts and McCulloch were not sufficiently sympathetic to socialism, so far Wiener was concerned. (Apparently Wiener, explains Lettvin, travelled with his wife to Mexico to visit Trotsky.) Lettvin wrote that the dislike Wiener's wife had for McCulloch was the last straw in a strained relationship, compounded by other misunderstandings.
Furthermore, McCulloch was not particularly bohemian in any way, so far as Alex Andrew, a younger member of the group Wiener split, recalls in an article in Kybernetes. He and his wife were of very wealthy families, Andrew recalls, although their wealth was strongly decreased over time. Andrew does not say anything about any Bohemian behaviour of McCulloch.
Lettvin argued: Pitts was the only one in the group who was dependent on Wiener for funding and help in academia after Pitts and McCulloch left Nicholas Rashevsky at Chicago to work with Wiener. After Wiener broke off relations with the McCulloch group, Pitts was put under a lot of stress.
