As much right as you to to complain about it.

It's like being on a crowded bus or subway car -- do you think those people squeezed in a standing position paid less than someone who is sitting down? Or have less rights to space or seating? How much right do they have to "encroach" on your space sitting on a bus while they're standing in the aisle or sitting in the seat next to you, being encroached on by someone else standing in the aisle?

Economy sections of airplanes are now like riding a bus, and in rush hour they are overcrowded. Deal with it - either accept it, or pay more to travel with more space.

Many are not even "big bodied" people - even many average (and healthy-sized) people don't fit in economy sized seats on most airlines today. Airlines have decided to fly cattle cars, and you can either accept it for what it is, or pay more to have a different experience.