Big deal Bengerman. The bad guys were never invited into Flight Decks. Don't you trust your own judgement? With your wife or kids, for example?
(You are not a Captain, nor an FO)
Judgement has nothing to do with it, there are regulations in place which, however stupid, MUST be complied with unless there is an overriding safety reason not to do so.
Your last comment is childish and incorrect
As the CEO of Virgin was on the flight, and no doubt complicit in Mr Diamond going onto the flight deck, it would be difficult to discipline the Captain, without the CEO disciplining himself!
So who was the legal commander of the aircraft?
The fact that this discussion is going on is worrying. Yes the regulations are crap, but they exist. It is not a matter of judgement or common sense, if you allow ANYONE on your flight deck who is not legally entitled to be there then you are in violation of national regulations.
It does not matter if the person is some tosser of a banker who happens to be best buddies with the pope, or your own wife and kids, THE RULES ARE CLEAR!