You could lose readers because of your genre, your voice, your characters, the author's gender/politics/age...who cares? You can't write a book worrying about not alienating people for any reason, let alone profanity, or you'd never get the book written.
You're never going to entertain everyone with the same book, so it's a waste of energy trying. It's better to write a book you would enjoy reading and to be true to the story, not pandering to the preferences of a group of people you don't even know.
I know the swearing in my books would offend people...but I also know there are other people who won't be offended, and so will read what I produce. And it's those people I care about, not the ones who choose not to read me. Life's too short to worry about people who don't like what you write. I'd rather concern myself with those who do.
