Passage revolves around a seat. Seat assignment. Seat numbers. Seat belt. Seat upgrades. Clearly demarcated seat areas (arm rests). Place small items under the seat in front of you. Tray table and other controls that correlate with a seat. It is all about a seat, not transportation of a person irrespective of size. If you don't fit in the seat you leased (not really purchased -- maybe rented?), this is a problem -- you need to lease more space, as in two adjacent seats or a larger seat (as in a higher class of service).

I really don't understand how this is debatable -- this seems obvious and factual to me.