I don't care if it's obesity or just sheer size..... if you cannot sit in a standard economy seat without intruding on the space of those seated next to you ("elbow wars" for armrests excluded!
) then you need to make arrangements YOURSELF to ensure you do not inconvenience others...
Southwest (and some others apparently) enforce such "consideration" it by selling you a second seat....... and refunding it if it isn't "necessary"...
Good approach.
I was forced OUT of my exit/aisle seat on a QANTAS flight a few years ago - LAX-SYD (yup.. 14 hours!) by an immensly obese man.... Had I stayed in that seat - constantly leaning to one side to avoid the parts of him that rolled OVER the armrest into "my" space, I would have needed a backboard and stretcher to deplane.... ended up in a bulkhead seat instead with zero leg room....
If whining about that means I will be seen as "lacking civility to fat people" then that is a title I will happily accept!
P.S. It was the cabin staffs lack of assistance in that situation that put me off QANTAS big time!