The airlines know that nothing sells tickets better than cheap fares and cheap vacation packages so that is a major factor in how they price tickets. Then in order to be profitable they load up on fees.
Good fees are optional fees that allow the airlines to generate more revenue by offering value added passenger services. Examples of good fees:
Offering wireless Internet connections while en route.
Providing seats with additional legroom makes sense for people who value the added comfort.
Giving special treatment such as allowing passengers to cut to the front of the boarding line, using airline lounges, or special screening lines.
Bad fees are for services where the customer has little choice but to pay:
Charging customers extra when they arrive at the airport to get seat assignments vs. waiting until minutes prior to departure to be given whatever seats are still available.
Paying a convenience fee when you purchase a ticket using your credit card. Allegiant Air and Spirit Airlines have started charging this fee.
When it comes to paying to check a single bag, some will argue that this is a fair charge since they would argue that customers who only have carry-on luggage should not have to pay (via higher overall ticket prices) for others who check bags. However, some feel that given the security liquid and gel limits that passengers should be able to check their first bag for free.
The only hope passengers have to influence airline fees over time is to do your best to avoid airlines who charge bad fees.