At the Atlantic recently (workaround archive link avoids paywall) Ariel Sabar tackled anew this old question, known to biblical students like me (graduate theological degree, undergrad in classical languages): Did Morton Smith forge The Secret Gospel of Mark?
Tackled anew because of a 2023 book by Geoffrey Smith and Brent Landau. Since titles can't be copyrighted, theirs is also "The Secret Gospel of Mark." They make the claim that the cover letter (remember, Smith never claimed to have found Secret Mark itself) was not by Clement of Alexandria, but also not a Morton Smith forgery, but rather, written in early Byzantine times by monks at Mar Saba to try to backdoor-justify same-sex monastic relationships.
There's no doubt that in what became the Orthodox world, as well as what became the Catholic world, such relationships existed, and if not common, were certainly not on the fringe, either.
But, would an invention of even a slice of a heresiac gospel have been the tool to do this? Doubtful. That's in part given that no such actual heresiac gospel appears to have existed. It's never mentioned by Eusebius, Ephiphanius in his Panarion compilation of heresies, etc.
Sabar, without mentioning all the relevant church father names, touches on the basics.
One thing he does not mention is epigraphy. At Biblical Archaeology Review, in 2009 renowned paleographer Agamemnon Tselikas discussed the "Clement" letter from that angle and essentially said that he can't prove Smith forged it, but he seems the most likely author. Ehrman and others have said somewhat the same.
And, lots of discussion, much of it semi-informed, at least, at the
Early Writings site. (There's also some backbiting.) A lot of it discusses Tselkas' analysis. He says that Smith misread the Greek he had in his photos, and that it's actually "naked men with naked man," not "naked man with naked man."
OTOH there? Although people call Tselkas the bomb of Greek paleographers today, what if he got this one wrong? Per another poster at Early Writings, almost all the accents in this photograph of Smith's actually are over consonants. So, that could be an accent over a final sigma after all.
Here is a semi-critical "fair transcription" of the Greek, with page-by-page English translation, and with text-critical footnotes in the Greek.
As far as why? Short of a smoking gun of a love letter, Sabar reviews all the evidence to document that Smith had a long-term gay lover. Atanas Todor Madjoucoff was actually bisexual, getting married and having kids. But, Smith's suicide revealed he'd willed almost all his estate to Madjoucoff. He had a personal photo of him that, presumably for reasons of emotional choke-up, Madjoucoff wouldn't accept.
But Smith had two reasons to forget the "Clement" letter and create its backstory. Actually, three, partially overlapping.
He was known as being not just skeptical but cynical about religious verities. He may have been an atheist, though I don't know if he has been confirmed as that or not.
The second and related? He'd been denied tenure at Brown. Other universities wouldn't hire him. When he got on at Columbia, it was in the department of ancient history. So spite would have been a motive, but driven by two reasons, not just one.
Sabar does not reference, per a screed by the one one-star reviewer of the 2023 book, three scholars who had trod this ground before him — and two of them before BAR in 2009 saying it thought the letter was genuine, paleography be damned. This review of Peter Jeffrey's book is big. (That said, per a couple of lesser reviews, as well as one other 5-star, Jeffrey's background as Benedictine oblate must be taken into account.) Jeffrey and Carlson are both discussed in detail at Early Writings.
Flip side? Also at Early Writings? Per Origin's take on the story of Jonathan loving David more than the love of any woman, was a homosexual slant to Christianity semi-common in pre-Nicene Alexandria? I don't think that's likely. First, we would have heard more about it, and ditto with the Smith/Landau thesis if it leaked outside the monastic world. In addition, the "Secret Alias" arguing for the gay Alexandrine Christianity, in reality is Stephen Huller, and he is an idiosyncratic Bible scholar indeed if he thinks Jesus not only did not claim to be the Messiah but instead claimed to be the herald for Herod Agrippa II as Messiah. No, really! Per a one-star review, it's worse! He apparently claims that Mark the gospeler IS Marcus Julius Agrippa, as in Herod Agrippa. Given that none of the gospels were originally identified by names of authors, this wasn't "the Gospel of Mark" at the start anyway.
As for people trying to defend Smith still? I remember reading Helmut Koester's defense long ago. Wrong. (And the "great fool" is rhetorical, especially since he also claimed that Secret Mark came before the canonical. Maybe you wanted to stake out an iconoclastic exegetical position. In reality, he knows that gospels in general have tended toward "expansion" the later they were written. Witness Matthew and Luke vs Mark. Witness the Protoevangelion. Etc., etc.) Didn't read Crossan's, but he was wrong too. BAR itself? Not.Even.Wrong.
There's one other thing that repeatedly gets mentioned. Yes, Mar Saba is "cloistered," and became more so after Smith published. But, Smith never made an effort to go back there to be able to get, or try to get, the actual manuscript so others could look at it.
But, even more, I think the Smith/Landau tertium quid idea is a dead duck. Most likely, Smith forged this letter. There's a bare bones shot it's legit. A cover letter of letters circa 600-700 CE? No.