When I lived in Wisconsin, we had user fees at state parks. It bothered me when I first moved there, because it was the first place I had ever encountered this. After awhile, I got my mind around the notion that it was important to give the parks a revenue stream for which they wouldn't have to compete with the thousands of other needs in the state budget.
Wisconsin sold a $30/year pass for residents that allowed unlimited use of the parks for a calendar year. That's really quite a bargain if you are a heavy user of parks.
Yeah, free parks are better than pay-to-enter parks. But pay-to-enter parks are better than neglected or sold-off-because-they-re-too-expensive-to-keep parks.