I'm skeptical that baggage fees have a lot to do with people bringing carryons on board. Business travelers typically don't personally pay for checked luggage and many are exempted anyway because of frequent flyer programs. Yet most just take carryons for the flexibility and to save time--and because they usually know how to pack efficiently. When I walk through the departure level, most of the people I see lined up to check vast piles of suitcases look mostly like families traveling.