Had to check this thread to see whether the question was photoshopping it into or out of images! Photographers are well aware that images with trash in can be good sellers and we now show off about taking worthy ‘environmental’ images in the same way we used to humbrag about competition wins. I even hear stories (dunno if they are true) of photographers staging photos of marine life interacting with plastic etc.
To get back on point - I think the most important thing to consider with manipulation - is if you do it - be open and honest about it (including a note about it in the image caption). I don’t think most people have an issue with photoshopping - as long as they are not misled.