In late August, American Airlines announced that it was suing an airfare website that sells seats using a sneaky money-saving trick — one that is forbidden in almost all airlines’ contracts of carriage. It works like this: If the airfare from, say, Boston to Houston is $400 on a nonstop flight, but on the same day the fare from Boston to San Antonio with a connection in Houston is $300, some people buy the connecting flight instead of the more expensive nonstop and get off in Houston. Their seat to San Antonio remains empty. So why is this, arguably, immoral? First, the airline loses money on ...