Well said Rainboe.
As a now retired F/E my experience of 'Flight Deck Visitors' hasn't always been a pleasant one; especially when flying a holiday charter flight! There can be nothing worse than having a passenger bum shoved in your face whilst they try and get closer to the businness-end of the FD. I'll also concur with Rainboe about the father wanting to bring his six-month son onto the FD and then to proceed in pointing out the various controls to a son who doesn't understand a word about what he's talking about... actually, neither did the father; yet another aviation Geek!
In an aeroplane such as the L1011-1, all of the passengers can see the constant stream of visitors to the front-end; not to mention those queueing for the forward toilets; until, eventually, you'd think this was a queue for a ride at Disnyland.
To be fair, there were the odd few visitors who showed a genuine interest in how we did things; except that they were few and far between.
Ultimately, our visitors became a huge distraction from the task that we were supposed to be doing; safely flying from A to B. I would eventually call a halt to anymore visitors to the FD, but would often be rebuked by the Skipper for being a 'spoil-sport'.
In later years, whilst flying the B747-200, it became less obvious that visitors were on the FD. Nonetheless, all that seperated the FD from the upper deck cabin was a curtain; which didn't prevent the odd drunken passenger from bursting into the 'office' unannounced.
The 'Good 'Ole Days' have long gone, but the terrorist threat cannot be ignored... I wholeheartedly approve of a locked door. That being said, the rules are somewhat 'over-the-top' in preventing an off-duty crewmember from using the seat to get back home after a long duty-day.
As for FD visitors; it should be the Skippers descision and not a blanket rule as decreed by the DoT. However, given that all FDs are now crewed by only two pilots... I'd rather not have any visitors at all. Bah Humbug.
TCF