Flares - they just bounce off the person (I handled a case involving a little boy who accidentally shot his sister in the face with a flare gun - her only physical injury was a cut, on the nose, from the plastic wadding).

Cockpit doors - I understand the current passion for lockable cockpit doors. However, in the case of Egyptair, Thai (I think) and maybe some others, the risk was *inside* the cockpit door, not outside.