No, it's not a "fringe internet thing". Many academics (and others) have been writing for over a century now, explaining why they think the biblical description of Jesus could not have been that of a real living figure.
In fact, iirc even the pro-HJ side have themselves several times noted in these threads that even at the time of the biblical writing (first few centuries AD) some people were disputing that Jesus was ever a real person, and saying the Christian beliefs were myth.
We have to be careful regarding the use of the term "mythicist" because it has been applied to people who said there was a flesh and blood Jesus in the 1st century:
David Strauss
"The gist of his position was in a large measure like the
mythical theory of David Strauss, which created a sensation fifty years ago.
Strauss held that there was verily a historic Christ, but that a vast mass of miracle and supernatural wonders had been woven like wreaths around the head of Jesus. Drews goes further. He alleges that there never was such a person as Jesus of Nazareth."(The Times (1910))
Sir James George Frazer
"
My theory assumes the historical reality of Jesus of Nazareth" (Frazer, Sir James George (1913) ''The golden bough: a study in magic and religion'', Volume 9 pg 412)
"I especially wanted to explain late Jewish eschatology more thoroughly and to discuss the works of John M. Robertson, William Benjamin Smith,
James George Frazer, Arthur Drews, and others,
who contested the historical existence of Jesus. It is not difficult to pretend that Jesus never lived. The attempt to prove it, however, invariably produces the opposite conclusion." (Schweitzer, Albert (
1931)
Out of my life and thought: an autobiography pg 125)
G A Wells. Jesus Myth (1996) and later works
Jesus Myth (1996) and Jesus Legend (1999) are labeled as examples of the Mythical Jesus Thesis (defined as the idea of "Jesus tradition is virtually--perhaps entirely--fictional in nature" (sic)) in Eddy and Boyd's 2007 ''The Jesus Legend Baker'' Academic on pp. 24.
"The year 1999 saw the publication of at least five books which concluded that
the Gospel Jesus did not exist. One of these was the latest book
(The Jesus Myth) by G. A. Wells, the current and longstanding doyen of modern Jesus mythicists."(
Doherty, Earl "Book And Article Reviews: The Case For The Jesus Myth: "Jesus — One Hundred Years Before Christ by Alvar Ellegard" review)
Christ-myth theorists like George A. Wells have argued that, if we ignore the Gospels, which were not yet written at the time of the Epistles of Paul, we can detect in the latter a prior, more transparently mythic concept of Jesus... (Price, Robert M (
1999) "Of Myth and Men A closer look at the originators of the major religions-what did they really say and do?" Volume 20, Number 1 (Winter, 1999/2000)
Free Inquiry magazine)
"In recent years the existence of Jesus has been debated heatedly on the Internet. The most thoroughgoing and sophisticated statement of this theory has been set out in five books by G. A Wells;
the most recent is the Jesus Legend (1996) (Stanton, Graham (2002) The Gospels and Jesus. Oxford University Press, p. 143.)
"Books by Contemporary Scholars
Defending Ahistoricity:
(...)
George Wells, The Historical Evidence for Jesus (1988); Who Was Jesus? (1989);
The Jesus Legend (1993); The Jesus Myth (1998); Can We Trust the New Testament? (2005) (
handout for Richard Carrier's 2006 Stanford University lecture "Did Jesus Even Exist?"])
This sampling over the course of 100 years shows the problem with defining the terms "mythist" and "Christ Myth theory"--
the terms have been used with people have accepted the existence of a flesh and blood Jesus in the 1st century but do not accept the Gospels as an accurate description of the life of that man as well as those who say there is no flesh and blood Jesus to be found.