I think I understand where you're coming from, but I don't think we'd have many planes left flying if we started putting that responsibility on doctors. They'd end up grounding pilots on the slightest indication to ensure that they couldn't be sued later.
This whole thing happened because of a knee jerk reaction to 9-11. It is an incredibly rare occurrence and one largely rectifiable by ensuring there are always two people in the cockpit. Mechanical (or electronic) failure and pilot error are by far and away the highest causes of airline deaths. I think these are still the areas to focus on rather than trying to prevent another Lubitz with another knee jerk reaction.
