Sorry, janea, I missed that you hadn't read anything of JP's.
The "appearance" of his endorsing that T-shirt is very shallow, I think, given the circumstances of the meeting and greeting, his support of free expression, which must include support towards the free expression of ideas one disagrees with if it is genuine, and this that he said (because people pay and often travel very long distances to meet him): ""Every single person that comes to meet me I want to be present for."
As I've already said, the rescinding by the Cambridge faculty seemed to happen before they knew about That Photograph.
Yes, I would say your conclusion about JP does support the bandwagon theory. I've had trouble finding the relevant sections of the book I'm reading on my Kindle. Not got the full hang of bookmarking and highlighting, etc. But the bandwagon theory, as I understand it, is about the importance of the social rewards (things like peer approval) and punishments for expressing 'right' or 'wrong' preferences in public interactions. This is a description rather than a criticism in the book. We are, after all, very social creatures with a need to conform with our peers if we are to feel comfortable.
I found one of my bookmarks. Blackford says: "Speakers want to persuade, and they certainly do not want to be dismissed, even demonized, without consideration of what they are actually trying to say." I think this is happening to JP. It has occurred to me to wonder if this sort of thing is more likely when a person appears to have a sort of fan base, as JP seems to. I can remember other Gransnet discussions, for example about what Richard Dawkins was saying about something or other, where there was the same sort of reaction.
With regard to Boris, I can't say I've ever wanted to find out much about him or to listen to his outpourings, as you put it. Perhaps what I have heard him say has simply been uninteresting. I seem to remember that he got the biggest audiences at the last Tory Conference, or was that somebody else?