<< 13)Shoulder belt seatbelts >>

In a crash, the plane doesn't stop suddenly (like an automobile). It's going too fast, and it usually crashes along the ground, not into a wall. Also, you have to lean over your knees to keep your head from being hit by pieces of plane during a crash landing, which the shoulder belt would prevent.

Anyway, my take on this carry-on mess is this: allow exactly one carry-on to be placed in the overhead compartment (subject to size and weight limits). If you want to carry on two items, you must put one underneath the seat in front of you (bulkheads excepted).