As a long time pilot of the emerald green aircraft, who has operated the 2 person in cockpit rule since shortly after 9-11, I am amazed at the negative tone of this discussion.
I filled out the recent EASA survey and am very much in favour of having a second person in the cockpit at all times,if only to make sure I can get back into the cockpit at all times. This policy has never caused any safety issues, and I personally cannot see what the issue is.