basically a lose/lose/lose situation for BA. Having seen several articles about this person, there would be 3 outcomes:
1: the one that happenned.
2: BA say it is ok for him to wear it, so he tells press that BA have no security issues.
3: no-one notices and when he gets off he says BA's security is appauling as they don't check their pax well enough.
Why on being challenged he just didn't remove it for other passengers and crews comfort explains just who he is. He wanted to create a scene, and he managed it. Any normal person will understand where the crew and captain were coming from and the sensitivity of the issue and would just comply, I think he got just what he deserves, and feel sorry for BA that they had to be his next victim.