Weight is largely irrelevant. The difference between a airliner full of 45Kg people versus 90Kg people constitutes about 5% of the total plane weight. Some fuel savings but would not be worth the aggravation, client humiliation, lawsuits etc.
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.
> A passenger takes up a seat regardless of how large he is
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...
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.