Why is it necessary? I don't understand. I'm not talking about words like "damn" or "ass." Those are crude but not as offensive as the ones I am thinking of. Since I don't swear, I am not going to start now by saying them. I don't think I really need to.
It takes away from the experience for me when a movie that is otherwise very good, with an interesting plot, a talented cast, and excellent scenery and special effects- think The Departed- is littered with the f-word.
Does it really add that much to the film if there's a lot of swearing in it? In my opinion, absolutely not. I don't understand why a screenwriter would choose to employ them when there are so many other words in the English language?