David Mo
Well, perhaps it my English that falls short.
Another thing is if you want to deny that consensus exists. Sorry, that four or five scholars deny it does not mean that there is no consensus. Another thing is that it is valid or not.
I accept that the baptism is one of the few specific biographical events that most participants in the "scholarly HJ consensus" agree upon. So vast is this consensus, that I can accept that there is diversity among the participants as to why each person thinks this event really happened.
Where there is diversity in reasons, some reasons will predictably be better than other reasons. It is especially likely that some of the reasons offered will make sense only in light of other commitments that the person has.
A person who argues that a baptism for Jesus is a remarkably unexpected development in the synoptic Gospels also likely believes that John's baptism was a token of having previously sinned, rather than Josephus' black letter testimony that it was a badge of righteouness having been achieved. Such belief, then, attributes a motivation to John's baptism which, by an amazing coincidence, agrees with Christian theories about the effects of that group's own (adult) baptism.
In other words, even though the conclusion may be factually correct (perhaps John dunked Jesus), and even if it is incorrect, the conclusion is still widely believed, nevertheless
this line of argument is a hash of later religious belief retrojected onto a pre-Christian ritual. Thus, this line of arument is, at best, suspect as a reason for offering the conclusion.
Personally, I think a baptism is somewhat likely. I gave reasons why I think that there was some influence from John's movement to Jesus'. If so, then a baptism would be a usual thing. However, much of what meager confidence I have about the event depends on Josephus' testimony that there actually was a real John to do the dunking. That testimony includes an explanation of why John ever dunked anybody. I can hardly look to Jospehus for reassurance about the reality of a key man, and disregard what Josephus tells me about the man's teaching.
Since I also accept that you were reporting somebody else's argument, I do not impute the argument to you. However, it is permissible for me to remark upon other deficiencies in that argument, in addition to or complementary with any critiisms you might advance.