People seem to forget the primary goal and benefit for all national parks, forests, state parks, COE land, and BLM land is to protect the wilderness and watershed areas.
If we lose those, we lose our ability to survive - paying a fee to maintain those areas creates a life-sustaining environment for all of us. Regardless if you enter or not, taxes provide part of the maintenance, the rest comes from fees of the campers, hikers, and those that simply stand in wonder at the beauty Mother Nature has created.