Thats fairly easy to explain, consider the following.
The word photography derives from the Greek (phōtos), genitive of(phōs), "light" and (graphé) "representation by means of lines" or "drawing", together meaning "drawing with light".
Now, cloning out is editing pixels..NOT drawing with light so is therefore an image not a photograph.
If there is litter in the scene then I would suggest you walk to it, pick it up and remove rather than cloning out later in post processing. Set your scene rather than make it in Photoshop or other editing programme.
Its much the same as a Photographer will walk towards the Bride and straighten the hem of her dress or turn the bridesmaids slightly one way before taking the photograph, they are setting their scene and not relying on post processing to make the shot.
Incidentally, Its my opinion that PP is required as even todays modern cameras are still not a patch on film of yesteryear.
If I cannot remove something due to dangerous circumstances then it stays in the shot.
Steve...
