This is very true. Here in San Diego County, for example, we went from a lot of shootable areas on NF lands, to a complete closure in the last few years. While I don't like the idea of restricting my use of public lands, once you venture into one of the public "shooting areas", you see first hand why it happened. The volume of trash is unreal. Shells, food containers, bags of trash, shot up electronics and appliances, old targets, diapers, furniture, etc. It is truly disgusting.
I don't understand it, but feel that is has to do with some folks from urban areas, who operate on a different relationship with the world around them coming out to the "woods" to play. I also see it every darn year when we get snow in the local mountains, you go up to hunt, and every pull-out, parking area, picnic spot, etc, is just strewn with garbage from the folks who come out to play in the snow. Bothers me to no end.
We have to police our own ranks. Respect for nature is a fading thing in the general population unfortunately.