First, Mark Bousquet ran the article Genre Fiction: To Curse or Not to Curse, That Is the Question, in which he states:
"Since then, I’ve largely kept curse words out of my stories. My go to swear word is “damn” because that’s a soft curse word, in my book, and I’m sure the occasional “shit” and “piss” has made its way through to publication. Part of this is a choice on my part to not use that kind of language (and if you think that’s a prude thing, you missed the demonic orgy in this book), but again, it’s mostly about what the right words are to come out of a character’s mouth."
A few weeks later, Lance Stahlberg, a former Shooting Star Comics alum and fellow pulp and genre writer, through his two cents into the discussion with his article To Cuss or Not To Cuss. In that article he writes:
"...in the crime novel I am working on, I'm up to 48 F bombs and 78 variations of feces. I even drop the dreaded N word. Twice. Two and a half if you count the time someone started to say it and was shot before he could finish it. Earlier drafts have an even higher curse per word count ratio."
Then I found that Lance referenced this article, Why I No Longer Swear in My Books, by Robert Chazz Chute, a writer I was unfamiliar with up to that reference. He adds to the discussion with this bit:
"The f-word can be a crutch.
"Use it too much and dialogue risks a feeling of laziness and sameness. Increase the frequency and the impact suffers. Working around that obstacle has proved so minor, I wish I’d done without cursing from the beginning. “She cursed him as she sliced his throat,” can serve just as well, or better, than a string of expletives."
So, where do I fall on this topic? What do I feel I can add to it?
Precious little, I'm afraid, but I will say that the following is how it works for me.
Gratuitous-ness is a relative thing, a sliding scale. As with any kind of possibly gratuitous content, be it sex, violence, language, gore, it is necessary for as long as it keeps the story grounded and keeps the illusion intact for the reader. The very second it begins to pull a reader from the story because it seems superfluous it becomes gratuitous. I know that makes it an art more than a science, but it's the best way I can gauge it. Only the contract between the reader and the writer can determine the answer to that question.
You're writing for a market with rules about such things. Then you do what the publisher or the market dictates. Other than that, I stand by my first comment.
And that's my two pennies. As always, your mileage may vary.