In the USA, depressed pilots could continue to fly if their depression was treated by medication as of around 2010 (Don't know off the top of my head, when it became the case in Europe). The problem is, most depression now is treated by an SSRI, such as Prozac. As has been pointed out before in this forum, Prozac and drugs like it, occasionally cause people who may not otherwise take their own life or the lives of others, to do just those things (Not often, but often enough to be a public safety concern). I'm not thinking that depressed pilots shouldn't fly. In many cases of depression, one of the best treatments is to immerse yourself in your work, to get your mind off of of the depression or it's cause, whether it be piloting or playing football (after any needed time off).
It is too risky for a pilot to take Prozac or similar SSRI's. If depressed pilots must be medicated, they should take an amphetamine such as Dexedrine or Adderall, or an amphetamine analog, like Methylphenidate (Ritalin). These drugs may not help depression as much as Prozac and the like, but they don't have the danger to public safety side effect of suicide, while taking others with you.
A depressed pilot might not quite be "on his game". Crewmates and automation can make up for that, but a pilot on Prozac might be hell on wheels (or wings), while he flies the aeroplane into the mountainside.
Of course, the public may never know if Lubitz was on an SSRI, such as Prozac (aka: Fluctin, Fluoxetine HCL), but it seems likely he and many past mass murderers were on them.
I wonder if Jet Blue pilot, who went crazy on a flight and had to be restrained by passengers, was on an SSRI (Selective Serotonin Reuptake Inhibitor)?
Change the regulations. Prohibit the use of SSRI's for commercial pilots. Pilots and passengers are better off with an unmedicated depressed pilot than one on Prozac!