BB...Not exactly what I meant...
The thing you have to remember is that you are in charge not the pax....
If an item that has been carried on is not stored correctly or has a place to be stored correctly then it goes....simple.
I'm sure that if you tell someone that their precious laptop is either going under the seat in front or the bulk storage container in the hold then they will pick the the former...if they tell you they will not fly with your airline again that is their problem not yours....safety comes first.