Depends where you live, optimistically. Many public lands in the US have a policy that you can camp there for free. I've used a lot of these sites. Very often, they're fucking gross. Styrofoam and beer cans overflowing from the firepit is common. At one site I cleaned up a turd that could have been from a big dog, but was suspiciously human-sized. This happened all over the country. Many national forests now make their own exceptions to the free camping rule, and I have little doubt it's in response to this rampant abuse. The abusers are out there.
This is also a cultural thing. Compare the US to Australia for example, Australia is often remarked as very clean in comparison and the culture in Australia is to hold onto trash until it can be placed in the nearest trash bin and everything remains relatively clean in comparison (whether in urban areas or campgrounds).
Well, yes, culture is the main factor by which where you live affects cleanliness.
But the other problem in the US is that we don't have just one culture. Anyone who talks in public advocates the same pack-it-out approach to trash. That's the practice in the self-consciously outdoorsy subculture. But the people who leave trash in public campgrounds, I suspect anyway, live in an entirely different world with no realistic communication channels between them. Application to national politics is left as an exercise.
So people with disposable income leave less trash, but poor folk who go camping leave more trash behind? On the other hand you have Burningman (lots of disposable income) with at least stated goal of not leaving anything behind but drive in with gas guzzling large RVs or fly in with more gas guzzling airplanes... I don't know who is worse.
