I feel the same way you do. It seems a few bad apples spoil the whole batch. I used to plink in a couple area at a local wilderness area.But they built a proper range and now discourage unsanctioned plinking. The couple of places I used did get really messed up. All kinds of crap left there. It was my practice to bring a couple large plastic trash bags and pick up all the plastic jugs, cans bottles, glass, brass, trash etc. I'd fill two bags in no time.
Now the range gets trashed with the same stuff. I've done the same thing, cleaning it up, but what really pisses me off are the hillbillies who shoot up the Range Rules board, or the sign-in board, or anything else they think would be cool to shoot.
Just like anything else, if people would be more considerate, we could all enjoy the shooting sports, including plinking without worry of another shootin' spot being closed down.