A not-so-modest proposal
Here's an idea for the marketing gurus at the airlines to consider: charge based on the total weight hauled - whether human or cargo or a combination of both. If the real issue is fuel consumption, that's directly tied to the payload carried, not to the number of passengers or the number of checked bags.
Charging fares based upon the combined weight of each passenger and their baggage is much more easily justifiable than charging a flat fee per bag and per person. Why should a 130 lb woman with two fifty-pound checked bags be charged more than a 225 lb man with a 15 lb carry-on? He's responsible for 240 lbs of payload, and she's responsible for only 230 lbs.
Fare's fair? (couldn't resist)