In my experience people don't treat national parks with much respect.
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!)
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).
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.
I've found the biggest issue in preserving wilderness is helicopters and planes - they can easily cover large amounts of terrain in short time in a very noisy and intrusive manner.
In NZ, we try to a) ensure the 'front country' has facilities for easy access by day trippers and that b) the 'back country' is not disturbed by commercial operations.
In some parts, the balance tips further in one direction than the other - as an example, while walking the Milford Track[1], hardly a backcountry experience due to the very well developed tracks and facilities to cope with huge numbers of visitors, I still found the very frequent overflights by tourist charters detracted from the overall experience.
It was still gorgeous, but the continual drone of tourist flights for people who didn't want to, or couldn't walk the track, detracted significantly.
In my usual stomping ground national park, no commercial flights or landings are allowed, you can't even lead a guided walk. You still get the occasional private pilot flying through, and of course can't really do anything about the airliners flying to Australia, but the frequency is far lower than you find in the more commercialised areas like Fiordland or Aoraki Mt Cook.
The Department of Conservation has a policy of focusing commercial activity in areas tourists want to be in anyway, so that the rest of the conservation estate is largely preserved for NZ citizens undertaking recreational activities.
[1]: https://www.doc.govt.nz/parks-and-recreation/places-to-go/fi...
Roads through a park have all the same problems as logging roads for habitat disturbance, plus having people who like to stop or throw shit out the window.