One simple reason: What's fair for the goose is fair for the gander. As airlines keep cutting services, or adding on little charges for every little thing that they used to include in the ticket price (think food in Y, ticketing by phone, etc.), then the passenger should be able to nickle-and-dime right back.

As a consumer, I tailor my attitude toward small inconveniences to match the vendor. If I have a vendor that provides good service and doesn't nickle-and-dime me, then I reciprocate when mistakes happen. The degree of tollerance declines with the level of service, however.