I'm a bit of a prude... I admit it. I like my books, movies, media etc. to be fairly clean. I'm not opposed to a great romance, but I don't want to see/read/hear about their bedroom escapades. I can let an occasional cuss word slip by... but sometimes, it just gets to me.
For me, reading is like taking a walk through an amazing garden. It's captivating and enjoyable and then... well, sometimes you step in dog poop. That's what reading foul language is like to me. It seems to show a lack of creativity and intelligence for an author to stoop to such base, crass language. There are so many other ways to fill the pages of a book.
And I think it bothers me even more when the swearing is random. You're reading along and for no apparent reason, a character cusses. There's no anger, no frustration, no emotion behind it. Just throwing it in there for the fun of it, I guess. And it doesn't fit with the story. It makes everything feel disjointed and awkward for awhile. Like stepping in dog poop.
And there you have it. I'm a prude who uses dog poop to make an analogy. At least I changed it to a garden, instead of the same ol' dog poop in the brownies story...