Welcome to FT.

If you run a "search" on this subject you will find it has been discussed AT LENGTH before.

Lots of opinions, but little resolution. It does seem clear to me that at some point a passenger should have to pay for an extra seat, especially to the extent that the airline does not accommodate everyone to use the seat they paid for.

Drawing the line is obviously a problem. Does the airline have some responsibility to have seat to "fit the average plus" size passenger? Do they have a responsibility to have a size criterion for a passenger? If they are responsibe AND made some rules, would they enforce them? They do not seem to make any real effort in enforcing the carry on baggage rules they set.

Not good for anyone they way it is.

Maybe an economy plus seat, width, not legroom, is in order. Anyone can purchase at a prorata increase in price, rather than double. Some people would be required to purchase one (hight/weigh combo?).

While this is a very real problem for some large people and those force to sit next to them, it does not seem to get enough "complaining" formally to cause a change. Perhaps children, and "slight people" should get a discount if they agree to sit next to a "larger" person who would pay the difference?