........And airlines should also charge/tax stupid people. They would be extremely rich if they were doing so.
They already do... Ryanair.
£60 for each passenger per flight if they "forget" to print a boarding pass.
Accidently paying for something eg. travel insurance because you didn't take enough care when booking.
And charging people a lot more because they can't go to Spain for a fortnight without taking 20kg of luggage each in addition to the 10kg they have for free.
A fat tax or charging people more based on their weight is not right. The idea is that you pay less for being a more responsible customer in terms of your travel arangements and are all avoidable extra charges, it's not quite that simple when it comes to personal weight.
I think that anybody who comes to the airport with an overweight checked-in bag should not be allowed to fly and will not get refund. That way the airline gets the revenue from the passenger and reduces weight by not having the overweight bag(s) on board... or the passenger(s)!