I was referring to the overnight partnerships with FedEx and other couriers that many airlines offer at rates slightly lower than their 3+ bag fees. Ground shipments, of course, will almost always cost less. That's why I included "at similar speed." But yes, in some cases alternative couriers are better choices.
This is completely false in the context being discussed. The majority of the costs of baggage handling are incurred on the ground. The issue of luggage weight is typically concerned with infrastructure at airports not being able to handle abnormally heavy bags or cargo with odd shape, thus requiring additional attention.
You were discussing the matter of charging for combined weight, when in reality the weight of a passenger/luggage load is minimal to costs of handling the flight compared to the weight of the aircraft and cargo loads (on widebody routes). Passenger and baggage weight are not considered when fueling an aircraft; a full load is always assumed and kerosene is added based on distance, weather and winds, not the quantity fat people in the back.
And those loads are accounted for in fuel loads and accounting.
Sure, it burns more fuel. But the increase in amount used is so small that it doesn't matter. Adding, say 500kg for an abnormally high number of obese passengers, to an A319 is less than 1% of a difference and fuel burn will thus probably not be affected by even half of a percent. It isn't accounted for and trying to do so would be inefficient.
It does to the accountants. This "extra fuel" from weight issues exists in such low quantity that it's irrelevant.
The airline industry of 1950 was much less dynamic than it is now; today, planes are more efficient, have much increased MTOW, etc. The figures of average passenger+baggage weight are recalculated on a relatively frequent basis and implemented into the fare system, anyway. With modern, lighter planes, the total weight divided by number of passengers is, I am sure, far less. Add in cargo revenue, and it's a nonissue. 1950 came and went. Now is now and that's where the focus need be.
Collecting the data from each flight for accounting purposes, overhauling the system to a weight-based fare structure, adding necessary infrastructure and staffing to enforce such a policy, et al, would far outweigh the additional revenue. The resources would be better spent/invested in other ways.
I am simply saying that the weight of the plane per passenger is less today than say, fifty years ago. Indeed, an added pound today is more significant in marginal percentage than it would have been in 1950, but it's added cost is less significant.
They are completely different markets and are charged in different ways. It is in a way subsidizing passenger costs; airlines could simply raise ticket prices and forgo cargo to lower the amounts of needed fuel. Cargo doesn't cost more to transport due to increasing human weight. Human weight is billed to human airfare, cargo weight is billed to the shippers.
As mentioned earlier in this thread, it is indeed being paid for by someone else; that someone else paid for a more expensive, less restrictive ticket.