Photographers can turn into graphic designers, and that’s because they manipulate images so much that they no longer reflect the truth.
The editing equipment available today essentially gives a skilled photo editor the freedom to change every single detail of a photo, but a good photograph will not require an awful lot of editing. It’s easy to take it too far, perhaps overdoing post production until your subject no longer look believable, and good photographers know when to stop.
Sometimes it’s important to have your own rules on post processing, and whether you should remove or add details from other photos. Photojournalist will be very strict, because it’s important that their images represent the truth of a story, while studio photographers may have completely different rules.