In a perfect world I would agree with you 411a but all to often the only thing the back end are worried about is what the hotel is like and where is the best place to buy a duvet. The truth is, especially when we fly new airplanes where things rarely go wrong, that the crew does not get hands on experience dealing with problems. I would have more confidence in a crew who regularly flies a L1011 or something in that generation because they no dought deal with more problems.
I believe the front end crew are an important part of the team and if there is an additional barrier between us and them then communication is comprimised.
Our company has been installing these new doors for over a year now and i recently flew with f/a who never even saw the door yet. Our procedures dictate that a f/a may not enter the cockpit unless it is for operational things. This in my opinion may prevent them from bringing things up with us because it is not done on a regular basis.
So what is better, preventing rare hijack or trying to keep good crm?