Having spent 11 hours on a direct flight next to an obese chap who was overflowing into my seat and made the woman on the aisle seat swap with him so he could go to toilet easier I would happily agree to such paying extra for 2 seats. The luggage allowance doesn't fuss me though.
I think we are too polite over how people prepare for flights. When I was young I remember it all kicking off behind us because a woman asked to be moved to another seat as the chap next to her had horrendous B.O. She was seen to be in the wrong but why? You know you are getting on a plane sitting next to people yet don't take the time to wash properly.
Similarly those who arrive and hold the queues up with things they know full-well they can't bring through. They are tenderly assisted, often arguing as they receive such, then ushered through. Back of the queue until you work it out for yourself!!!