Well, luggage is weight, and weight means more fuel burned. That's not the scam.
The scam is advertising your plane ticket as $20 cheaper than the competition with luggage included, and then make you pay $30 for the luggage at checkout.
Traditionally, airlines would not charge for the first two pieces of checked luggage unless they exceeded weight limitation. But in February of 2008, United Airlines began charging $25 for the second checked bag. In July of that year, US Airways (LCC, Fortune 500) started charging $15 for the first checked bag
Well, luggage is weight, and weight means more fuel burned. That's not the scam.
The scam is advertising your plane ticket as $20 cheaper than the competition with luggage included, and then make you pay $30 for the luggage at checkout.
This was to offset high gas prices. Gas prices went down. Luggage charges stayed.