As in all walks of life!
The first time I walked up Snowdon, a couple of years ago, I noticed a young lady with a carrier bag who was picking up litter as she went along.
A light bulb moment for me, and I now always take a spare bag for litter, and pick up anything that I see, as long as it isn’t too yucky…
Except on the most popular routes, it is encouragingly sparse, and some of what I do find must be accidental - I have certainly lost the odd water bottle from a pocket, or had something blow away too quickly to follow.
So, yes, a few can spoil it, but a few more can help put it right again 
Adrian
G4AZS