So. Lufthansa appear to have said that here is no stopping a 'rogue pilot'.
To commit mass murder.
Sorry, Lufthansa. Not good enough.
If this is how you, as a company, feel, why would anyone risk their lives flying with you? Ever again?
Because it is a simple fact.
As unfortunate as it is, if somebody is intent on causing harm, either to themselves or others, and their intent is not known in advance, there is little that can be done to stop them. This applies to
anybody in
any situation or profession. All that can be done is to analyse what they did, and try to make changes to prevent re-occurrence of the same sequence of events. There will, however, always be a way - it is not possible to completely eliminate risk - in ANY environment.
The aviation industry uses the ALARP standard - As Low As Reasonably Practicable - in risk mitigation. This means that, whilst concreting pilots into the flight deck after boarding may be a way of eliminating the possibility of in-flight FD intrusion - it is hardly practicable.
And commercial realities often have to be taken into account when deciding what is 'practicable'.