A solution for one problem can create a separate and entirely different problem. Super secure cockpit doors have led to pilots being able to down aircraft when alone in the cockpit with no way for others on the aircraft to regain "control" of the cockpit. This anti terrorist door created the opportunity for those pilots who are unwell or misled to kill everyone on board for whatever reason they may have.
Perhaps it's time to rethink this strategy. Let's go back to regular doors and screen passengers better. Once you let on terrorists , having a secure door does not solve ALL of your potential problems. It is impossible to be reasonably sure another pilot is not going to use the opportunity of being alone in the cockpit to once again down the aircraft. But we need to ask ourselves if the problem of having pilots down aircraft behind secure doors is greater than the problem of terrorists gaining access to the cockpit. Which problem is greater?