You imply that humanity is intelligent, so I'll agree with your first sentence.
The idea of a fine or jail time would require that someone goes back through and obtain evidence that person A or person B did indeed leave an aircraft under an evacuation order with personal belongings. Plus, people still murder others on a daily basis knowing full well what the consequences are, so I don't think that will work.
From where I sit as a Captain who may possibly have to give an evacuation order one day, I don't care if you have treasured belongings in the overhead bin or even a small bag with insulin, as was previously mentioned - chances are very high we are somewhere that can replace any or all of your things and guess what - you're going to the hospital anyways, so those medical issues you have can be looked after.
Instead, maybe we need to look at the way we describe an evacuation to passengers in the first place. Too many times these safety messages try and convey a sense of calmness or hilarity to a situation that will be anything but. To someone who has stood beside the burning hull of an aircraft watching two of their friends die, I can tell you that I cringe when I hear someone joke that "there are many ways to leave your lover but only four ways of leaving this aircraft" or other form of similar filth.
I think we go the very hard road and actually describe to people during a safety briefing exactly what will happen and what the consequences will be, for example "In the event you hear the command evacuate, evacuate, evacuate, you will release your seat belt, stand up and proceed to your nearest emergency exit without pause or delay. Failure to do so may cause you or those around you serious bodily injury up to and including death. Your flight attendants are pointing to your nearest exit now."