Why not charging by passenger weight then?
Completely appreciate there's no fair way to police it (other than that, I think Samoan airline, who charged based on the person/bag weight combination), but I think it's indicative of it all being a bit of a sham. Of course weight increases costs of flying, but is an extra 1kg in a checked bag really worse than carrying 20/30kg more of fat or muscle?
What it boils down to is volume and time. A passenger takes up a seat regardless of how large he is (...) so he's charged for a seat. Luggage changes that equation far more than passenger body weight.
I'm only halfway joking when I say I've lost many an elbow into the side of someone substantially larger than I. For some "a seat" is "their seat + several inches of mine".
I know it's not really the problem at hand, but it's poor proxy for volume, and again, just shows that the weight fee is just a sham.
Just going to start manufacturing a "flight jacket" with pockets for all your luggage...
Already there...
https://www.skyscanner.net/news/best-wearable-luggage-jacket...