So how many people lost their lives because passengers wanted to take their hand baggage with them during an evacuation? I don't remember a single case. I think the problem is overblown. It's understandably causing anger, because those taking their possessions are endangering not their own, but other passenger's lives, but the actual damage is next to none.
Addressing pilot suicide is much more important from the safety point of view. There are two men and a fire axe behind a bulletproof door, so a crazy pilot is still able to kill his coworker with the axe and then everybody else by flying the plane into the ground.
A punishment for passengers taking their hand luggage with them isn't going to help anyway - under stress (both from the evacuation and from the perspective of losing documents and valuables), no one will think about it.
A good beginning would be to tell passengers before the landing to have their passports, their money, their mobile phones and their keys on their bodies - because in the event of an emergency evacuation, they will not be able to take these items with them. I surely do this before every landing. But then, lots of people will probably complain about being told about such a possibility at all.
Also, pax should be told to leave their stuff on the plane in case of an evacuation in the safety briefing before the flight - many carriers don't say that. So how are people supposed to know? Yes, the safety card in the seat pocket says just that, but apart from aviation geeks, probably no one reads it.