I don’t know nearly enough to judge whether carrier is rigorous or reliable, but having read a couple of his books, it made enough sense for me to basically dismiss the question of whether or not anything about Jesus was based on a real guy. I’ve not seen proof that he was, though I recognize that given the languages and historical contexts involved, the field isn’t one that lends itself to armchair speculation.

Something I can say is that most of the scholars are religious, and most of the ones who aren’t still were raised religious. It’s obvious that there are a lot of preconceptions being thrown around, and a lot of overtly religious people muddying the waters.

There’s not many scholars because mythicism is nuts.

Literally the earliest primary documents we have are a set of letters by someone known to be persecuting followers of Jesus (in areas he had authority) writing to areas he doesn’t have authority to persecute in, claiming he’s joined the cause, telling them to ignore other versions of Jesus or other gospels, and acknowledging his peers are claiming he and his followers are doing evil in the name of good.

You just don’t see that within decades of a mythical invention of a religion. Those other versions of the tradition have clear and concise beliefs reflected in Paul’s opposition to them which line up with popular apocryphal texts likely dated to the first century.

This sort of split is seen over and over with cults built up around a real person within years of them ending up imprisoned or dead.

What’s typically seen with mythical figures instead is syncretism where the legends combine and grow. It’s not “no, Dionysus didn’t conquer India, he was instead kidnapped by pirates in the Mediterranean” but “oh, he conquered India too? Did you know he was kidnapped by pirates?”

This only happens for Jesus much later on. The early days are characterized by infighting and schisms. It’s nearly what all the letters and nuances of the gospels are about. “Oh, he said this parable in public - but then in private he told us it was really about X.” “There was a race between that unnamed disciple and Peter and though the unnamed guy got there first, he waited and it was Peter who went inside the tomb first.” “That Thomas guy was doubting he physically resurrected but then changed his mind.” “They wanted to claim the seat at his right hand in heaven, but he said the last would be first and it was reserved for someone who was slave to all (like Paul, the last apostle who said in his letters he made himself a slave to all).” “Hey Corinth, why did you depose Rome’s appointed elders? Also, isn’t it awesome when young people defer to the old and women keep silent?”

Additionally, the mythicists are so dogmatically committed to their views that it interferes with their scholarship. So as an example Carrier thinks the mentions of cosmic generative seed in Gnosticism relates to a “cosmic sperm bank” rather than recognizing it as the influence of Leucretius’s “seeds of things” from De Rerum Natura where 50 years before Jesus is born he happened to describe survival of the fittest and naturalist origins of life as randomly scattered seeds which develop into the life we see by way of what survived to reproduce, even describing failed biological reproduction as “seed falling by the wayside of a path.”

Which is a much more interesting angle for a guy who goes on to have a canonical “secret explanation” for a public saying about how only the randomly scattered seeds which survive to reproduce multiply and the seed that falls by the wayside of a path does not. A parable located in apocrypha right after a saying about how no matter if lion ate man or man ate lion man would be the inevitable result and how the human being was like a large fish selected from many small fish. That apocrypha elsewhere seems to refer to Leucretius’s ideas and even explicitly calls the idea that spirit arose from flesh the greater wonder compared to the idea flesh arose from spirit.

But no, instead he could only see a cosmic sperm bank because the idea canonical Christianity was a conservative retcon of a very different early set of ideas would have meant it likely there was an original historical figure with those transgressive ideas that needed to be reworked with things like secret explanations in private for public sayings.

David Fitzgerald is another mythicist who has published a few books on the subject.