If you believed someone killed your child, would you be able to say oh well, whatever, and get on with it? This is what MAF believes, and no amount of grief counseling will likely change that.
It would be interesting to learn exactly why MAF believes what he does -- I seem to remember that someone described to him someone who was at the scene of the accident at most within minutes, and MAF knew this man and that's what led him to believe it was no accident.
While there is no evidence that MAF is delusional, it was a mistake, if MAF was looking for credibility, for the film to go on & on about the Nazi family history of Prince Philip which is irrelevant. It was also a mistake to make any comment about some sins of the royal family going back 100s of years -- also irrelevant.