Apparently sociopaths can be detected with MRI scans. Ask some indirect questions to trigger responsibility and empathy and you will see their brain is dead silent in the part which should show reactions. I bet half of the AME's don't know what a sociopath actually is.
1) It's not obvious that Lubitz was a sociopath. Assuming he's guilty of killing all the passengers, there could be any manner of psychiatric illnesses that led to the crash. Just picking on the sociopaths isn't going to solve the problem.
2) What are the sensitivity and specificity of the test? That is to say, will it give you lots of false positives or negatives? The answer, almost certainly, is 'yes'. So what do you do with the (say) 10-20% of pilots who are wrongly labelled as potential murderers?
3) At least some authorities think psychopaths are unlikely to commit suicide. Think of the stereotype of a pilot. Cool under pressure, despite the huge responsibility. A lack of empathy might actually be helpful under some circumstances. Maybe you actually want psychopaths as pilots (but not bosses).
I'm being slightly tongue-in-cheek, but I'm not actually sure that you know what a sociopath is.
All doctors get some mental health training. Not a lot in comparison with psychiatrists who've specialised in it, but we've all seen things that few laypersons have. I was sent in to have a chat with a delightful gentleman who had come to see the psychiatrists because his paranoia was getting worse. After the interview I was told to have a read through his notes. He'd taken an axe to several of his colleagues a few decades previously.
In the UK, most AMEs are GPs and a fairly large proportion of a GP's workload will be taken up by people who have psychiatric illnesses, declared or otherwise. In my emergency department I see a few overdose patients every week.
Overall, I agree with the premise that AMEs are going to be quite limited in their ability to make a psychiatric assessment of prospective pilots, but I don't think a quick 'techno' fix is going to be the answer either. But don't be too dismissive of AMEs. They are rather likely to know more about psychiatric illness than
you.