Airlines can do whatever they want with fees, of course, and can even make a good argument for some of them, but I wish they would not bother trying to be disingenuous about the reasons for it. Here's a case in point: Virgin Atlantic is lowering its free checked bag allowance in economy for U.S. and Caribbean routes to one, down from two.
Why? To raise revenue? Perish the thought. In the Q&A section on its website, Virgin stated: "In order to remain competitive, we were required to make a change to the Economy allowances for the USA & Caribbean from the original policy." (That original policy was going to keep the limit at two.)
Required? Really? Who put the gun to its head? Normally, having to do something "to remain competitive" means having to offer something that the consumers want that competitors are offering. I'm willing to bet that consumers don't want the new bag fee, even if they understand it or at least are willing to accept it. I supposed Virgin Atlantic could argue that it needs to match other airlines on revenue-raising measures in order to compete on fares, but that would be quite a stretch for the wording they are using here.