In my experience people don't treat national parks with much respect.
You can have millions go through a a national park every year and 98% of the park will still be preserved with harmless any humans passing through.
Local example - Great Falls National Park (VA side). Proximity to DC means it's a popular place. Fine, the NPS keeps it pretty tidy. But, there are often cars backed up for a mile in every direction - the single entrance is a major choke point for traffic. This is despite the pay booth being a good ways down from the intersection - the cars just back up onto surrounding roads. The park is often full, so lots of visitors end up turned away (where they then move to one of 2-3 nearby parks with less facilities and ruin those with trash and feces).
These days I really do expect disrespect, at least to stand out as the perceived norm due to how much more common it seems to be. (It isn't really that common, but if you're in a crowd every day over a year, several hundred different people across a couple hundred days, statistics catches up!)
Compared to normal patterns of human land use (agriculture, living space, resource extraction), national parks, inundated-with-tourists-or-not certainly qualify as preservation.
As another poster said, 50 yards from the trails lie hundreds of square miles of wilderness that few visitors venture into.