Simple.
I am currently 26 and have been flying since I was 18, I will most likely move on to flying an A320 or similar when I am 29, not too dissimilar to this FO. Now by that time I will have more than 4000 TT and flown in no particular order:
C208b bush flying
GA8 para dropping
DHC6 airline
Q400 airline
I will have worked my socks off and sacrificed to get there, have two kids and a beautiful wife at home and been around the world.
Who do you want sitting in the RHS of your positioning flight? Me or the 200 hr cadet who's daddy paid for his TR? I highly doubt this guy has been radicalised or we would have heard someone claim responsibility, he is simply a selfish individual who has ruined thousands of lives.
Bring in the 1500 TT FAA rule and we can start fixing our industry.