There really needs to be some educating here with regards to the procedure of having a cabin crew present when a pilot leaves the flight deck.
It has absolutly nothing to do with stopping a pilot from doing something he/she shouldn't do.
You need to visually verify from the pilot seated position who is trying to access the flight deck. On some types of aircraft a CCTV monitor shows the seated pilot who is at the door.
Some types do not have this and therefore need a cabin crew member in the flight deck to look through a peep hole in the door so the pilot can stay seated at the controls.
Some airlines have adopted to keep this policy even if the type of aircraft has changed or been updated to allow a CCTV/Monitor from a seated position to be installed. But the origins of the procedure and the legalities of needing to do it are firmly routed in monitoring who is accessing the flight deck, not to prevent pilot suicide.
If it was a pilot suicide prevention procedure its got some rather gaping holes in it!