In my org. tho the FD is off limits steps are taken to mitigate the risks while crews visit the washroom. Something as simple as no pax in the vicinity of said washroom while the crew went in/out works quite well. To my knowledge none of our passengers ever objected when politely requested to defer to the cockpit crew. If a pax decides to hang around or move toward the fwd area then the door remains closed/locked/bolted til they are clear. If a problem arises in cruise that is serious enough for one of us to go back and have a look then the same rules apply. If we are "detained"
while back there? The other guy/gal upfront can still land somewhere close.
We seem to be focussed on 9/11 for the most part here. Tho that was perhaps the watershed moment we need to look beyond that and accept that bad things
can happen when unauthorised persons enter the FD. Can anyone recall the Nigerian (i believe) Airways B767 that was hijacked and ordered to fly well beyond the endurance of the aircraft? In that particular situation the crew was taken out of the decision making loop with disastrous results. By all indications the hijackers had no desire to destroy the aircraft or any property (though they claimed to have had a bomb), they wanted to fly to somewhere they perceived as safe. Had they been kept off the FD at all cost the crew would have had the opportunity to land somewhere safe and refuel/negotiate or whatever was deemed appropriate to secure the lives of those aboard.