Advent hyped the book as a "critical analysis of Heinlein's novels and stories, his style and technique, his strengths and his weaknesses, and his place in modern science fiction. It is a study in depth which is neither adulatory nor carping."
Heinlein hated it. Heinlein's animosity seemed to be directed more against Panshin personally as against the work. This may stem from an article Panshin had written for Shangri-L'Affaires about sexuality in RAH's fiction, and concluded that he avoided dealing with adult sexuality. Redd Boggs, who was editing Shangri-L'Affaires at the time, ran the article under the title "By His Jockstrap", mocking Heinlein's famous story "By His Bootstraps".
Additionally, while researching the manuscript, Panshin had also gotten loan of letters written by Heinlein to a recently deceased conservative fan, Arthur George "Sarge" Smith, to whom RAH had dedicated his novel Starship Troopers. Even though Panshin found nothing useful in the letters, when Heinlein learned of this, he was enraged at what he took to be an invasion of his privacy. According to one source, Heinlein threatened Advent with a lawsuit if the book were published. This caused Advent to temporarily postpone publication, however, several chapters of the book were subsequently published by Leland Sapiro in his fanzine Riverside Quarterly, and when no lawsuit materialized, Advent went ahead with publication of the entire manuscript.
A few years after the book had been published, Panshin encountered Heinlein at a speaking and book signing event in New York City. He was convinced that Heinlein had simply been misinformed about the book's contents, which was not at all anti-Heinlein, and wanted to make known that he was in fact a great admirer of RAH however, when he approached Heinlein, in an attempt to bury the hatchet between the two of them, he was frostily rebuffed. The exchange was witnessed by three New York fans, Gary Farber,
Ben Yalow, and Moshe Feder. Farber later remembered: "Panshin walked up and stuck out his hand, beginning an apology to Heinlein. Heinlein wouldn't let him complete his first sentence, interrupting him with the coldest 'Good day, sir.' and refusing to take his hand. Panshin tried several times, but just got his words interrupted with 'Good day sir.'. After several attempts, and Heinlein's utter refusal to even listen to a single sentence of apology, Alexei gave up."