An excellent point from the_hawk.
LGW you are over-reacting big time. An open cockpit door is not an invitation to disaster, would a terrorist be on each flight waiting for the time when a door just happens to have been left open for some reason?
Get a grip. I have never been distracted by an open door. Grumpy captains maybe, loaders, engineers, refuelers and dispatchers have distracted me from looking out of the window when I should have been doing something more useful, but just having a door open when everyone else is strapped in has never bothered me.
I don't remeber any precedents where a pax has suddenly tried to fly the plane because the door was unlocked, maybe you could furnish us with details of such an incident to back up your wild assumptions.