As a North Sea Helicopter Commander, we have an open cockpit and are unable to close it other than with a curtain. I am seriously thinking about moving to fixed wing, but this whole incident and jaded my view.
Having been a guest on the flight deck, I totally understand not wanting public access. Somebody mentioned "you have to be strong to deny access when crew members are being executed", well as an ex police officer....you do have to be strong, or look what happens.
Don't let them on board in the first place, talk to El Al on how to do that.
Safe flying to you all!