The whole discussion internet wide brings out some really nasty qualities in people since they need to make it personal instead of looking it as a fact based discussion.
Each plane has a Maximum Gross Takeoff Weight! Humans are figured in at an average weight with carry-on luggage. If they airline wanted to be fair they would need to design an adjustable seat and charge passengers per pound or kilo. Don’t see that happening anytime in the near future! Since you want a really heavy person to pay more someone very thin, should have to pay less than the average.
The bull crap in this whole argument is that this has always been figured in and most often balances out by the size diversity of the passengers. So this is just another typical American Greed argument. What God has to do with it is beyond my comprehension unless one is a fearful flyer and prays trough the trip.
If we want to pick on people for size on a plane my personal gripe would be big guys with big wide open thighs and overdeveloped shoulders who not only take up half my seat but also most of my leg room. Bottom line is I do not complain about sitting next to anyone, my mother taught me manners.