What an appalling loss of life!
Lubitz's hiding of relevant, potentially disqualifying personal information from his employer is a violation of the trust expected of a person in a critical occupation, but is also a very human reaction to threats to their livelihood and self-image.
The implementation of two persons in the cockpit rules is a logical first step, although it is not a perfect solution, to the cockpit access problem created by the 9-11 cockpit doors.
What is needed , long term, is implementation by regulators of a Human Reliability Program regulation. These programs already exist for people who do other critical actions such as with nuclear reactors. You can get a taste of what this type of program would entail here:
https://fmt.kcp.com/OSTfederalagent/Docs/HRP.pdf
The bad news is that there will be a personal cost and loss of freedom as well as program operational costs in $$. If the unions play their hands right, they should be able to at least generate some compensating pay for their members in the process of agreeing to go along.