Working Blue; or, the Use of Swear Words

There's a good bit of swearing in The Blessed Man and the Witch, mostly by certain characters.  Some of them swear a great deal, some don't as much, and others don't at all.  I included salty language for several reasons:

• I worked very closely with military veterans and law enforcement professionals for over a decade, and listened to how they talk.  Most of them expanded my own blue vocabulary in ways that were both hilarious and appalling.  It's part of that culture, like it or not, so I wanted to capture that element in my book; some of the characters, after all, come from military backgrounds.  If you want to write realistic dialogue, you have to listen how real people speak and model that.  
• A properly placed four-letter word can shock the reader and set the stage for what's to come next.  For example, one character, with little provocation, screams four-letter words at another character early on in the book.  It shows the reader that this person is unhinged without me having to say it.  It was startling and horrible, and intended to be that way.  
• When a character who typically doesn't swear starts using profanity, it shows how that character is feeling stressed or otherwise beleaguered.  Swearing can symbolize a loss of control.  I work very hard to keep from cursing in front of my son, but sometimes an ill-advised word pops out in the heat of a frustrated moment.  I'm pretty sure I'm not the only person who's done this.
• There are some characters I want you to like, and some I don't.  How they speak and what they say can accomplish one or the other.  I want them all to be interesting, yes, but some are just going to be more likable than others.  It's harder to like someone who's potty-mouthed all the time, including his interior dialogue/thoughts.  

The Blessed Man and the Witch is about the end of the world, or at least the beginning of the end.  It describes violence and other horrible events pretty graphically.  The kind of people who don't scruple to commit murder aren't going to be turned off by four-letter words, and are more prone to using them.  I understand entirely if adult language bothers you, the reader; there's a reason why it's usually kept out of budget meetings and presidential speeches.  But it is useful as a tool.  

A final note: I've noticed some reviewers on Amazon will lower the star rating of a book review because of the book's salty language, and in one case, I read the review of one person who said he's making it his mission to one-star every book that has four-letter words in it.  That's an extremely ill-advised thing to do.  A book review is intended to describe a book's merits (and demerits).  Using it as a vehicle to promote one's personal beliefs undermines the value of that review.  Think of it this way: you didn't mind all the death and killing, but you had a meltdown over the f-bombs someone dropped in the book.  Why?

TL;DR: There are sometimes good reasons to use four-letter words in your characters' dialogue.  Don't get bent out of shape because you read some.