The locked cockpit door issue of Germanwings is a diversionary side effect
No, it was one of the holes in the cheese that when aligned cause an undesireable event which could have been avoided because it was predictable from the outset! The new phrase is TEM; this is a pretty big threat and its not been managed; how many explosive decompressions are practiced with one person on the flight deck?
In nearly 50 years of aviation medicals nobody has checked my mental state, I have no idea who my GP is and he probably has no idea who I am. Every now and then someone will deliberately kill themselves in an aeroplane, virtually nothing we do will prevent it so we must ensure that this cannot be a contributary factor in endangering others. I recall an event where a Flight Engineer attacked one of the pilots with an axe; fortunately the door was not locked!