In principle, documentary photography does not allow for much change in post processing. You need to depict the reality as it is or as it was.
Since digital photography the public might be concerned by manipulation of images. In order to keep the trust of the public, the United States National Photographers Association adopted a Code of Ethics that says among others:
Ideally, visual journalists should respect the integrity of the photographic moment.
This means that removing distracting element from a scene, for a better representation of the subject is against the Code of Ethics of photojournalist.
Documentary photography and why converting to black and white.
Distracting elements can take multiples forms. We have learned through various articles on composition that brightly colored element attract the attention over other elements in a scene. Warm colors will draw the attention more than cool color. One of the ways to eliminate distracting element from a scene while staying true to the integrity of the photographic moment is to convert to black and white.
Initially, photojournalist did not have any other choice than black and white. The fact that we have this choice today does not mean that we shall carry colors with us all the way to the audience if colors do not serve the purpose.
In this picture, a white boat in a fisherman harbor is the main subject. Its name: Hakuna Matata contributes to the story. Hakuna Matata is a Swahili phrase that translate to “No Problem” in American English. The public in general does understand that fishermen are at risk when at sea. In this case, the name of the boat is a way to illustrate that his owner feels secure on his boat.
In the original color rendition of this picture, the group of lobster traps perfectly aligned in the back along with the Fisherman shed were very distracting because of their green and red color. In this Black and White conversion, the main subject, our Hakuna Matata fisherman boat keeps our attention.
When you want to cut distraction, try Black and White conversion. Most of the time, your main subject will gain visibility. Nobody will tell that you have questionable ethics. You can read more on ethics in photojournalism at dpreview.com. I also found this great article debating the use of Instagram by photojournalist very interesting.