I do NOT think that ticket prices should be based on weight, nor do I think that obese people should somehow have to pay more for their one seat. I know and understand from years of industry experience how airfares are calculated. It's very very complicated and boring and has nothing to do with weight. It isn't like taking a bus or the tube where you pay xx from zone 1 to 2 and xy from zone 3 to 5 etc etc. When you are on a plane most likely the person next to you has paid a completely different price for their ticket. I couldn't care less what someone else spent, I only care how much I did! There is no way the airlines would take the bet of charging by weight. How can they anticipate if the plane is going to be full of skinny 7 year olds or sumo wrestlers? Since pricing is based a lot around inventory, again it's back to how many seats will one passenger occupy.
I don't especially enjoy being pushed up against the large person next to me, but I also don't enjoy sitting next to someone wearing White Shoulders, or has just eaten garlic, or the air marshall who spent the whole flight staring down my cleavage. I also don't enjoy people who talk really loudly on the bus or fart in the lift. But such is life. Again this cannot be compared to sitting next to a passenger who simply needs two seats due to their size.
Unless you own the airline or have stock in it why would you care what other people pay? What I can tell you is even if obese people had to pay more for the 'extra weight' the savings wouldn't be passed down to anyone else. How do you know that the chubby person sitting next to you didn't already pay for a last minute, full fare ticket that costs the same as a business class fare? Would that make you happy?
Like I said earlier excess baggage fees aren't based on extra fuel consumption. Heavy bags cause damage to other peoples luggage, the luggage bin and employees. Hence the extra cost. Plus it's just another for the airlines to charge more. Why not, they are a business...
The reason hand luggage is limited is again because overstuffing the overhead bins causes damage to the aircraft. Also during bad turbulence large and heavy bags will cause the overhead bins to pop open, resulting in said bags to fall on passengers (I have experienced this).
Somebody asked if the "passenger in 32b would be forgetten in an emergency". No, they wouldn't be forgetten. But at 5"9 and 130 lbs I would not have been able to pull them out of their seat and drag them off the plane.
I really don't like fat bashing and am sure that large people don't really enjoyed being squeezed into a seat either.
Either a very large person will tackle the seat issue at the time of booking and book two seats or a first class one, or they'll chance it and see what happens at the airport.