There is a lot of one-man theories regarding early Christianity/mythicism that has made it into atheist circles and are quite widely believed to be true despite having very little basis in fact.
What I find most interesting is that the people who promote these view seem to hold the same basic view: The mainstream view on early Christianity, firmly believed to be true by virtually all experts, is false. Furthermore the mainstream view is influenced by Christians who are biased and untrustworthy and can therefore be dismissed as just confirming a pre-conceived idea that Jesus must have existed. Jewish, agnostic or atheist scholars who also believe Jesus existed are somehow forced to tow the line because their careers are build around the idea Jesus existed and they will loose their jobs and funding if they find anything different.
The people whose opinion should be trusted are therefore most often atheists and non-experts who, free from the confines of scholarship, are the only people who can "see" (and accurately interpret) the few details of the evidence that has apparently evaded thousands of scholars and confirm that Jesus did not exist. Much time is spend on explaining that it is just a happy coincidence that this happens to support their atheism and they are completely unbiased.
Sometimes experts in other fields will agree with their interpretations, or experts will say something which can be interpreted to support mythicism. In that case these experts can certainly be trusted despite otherwise being in strong disagreement with mythicism.
Finally the mainstream view Jesus existed is just verging on collapsing with more and more experts being secretly convinced of the mythicism position but are to afraid to speak out.
Interestingly this is exactly the kind of thing creationists say about evolution but that is TOTALLY not the same
I think Richard Carrier and Raphael Lataster are the leading exponents of these views.. Carrier for instance wrote a huge book where he computed the chance that Jesus existed to be something like 0.08% lol.