Looking at the Vine’s Dictionary, the New Testament definition of holy is long, with different Greek words that are used. I see two things that stand out: conduct, but also a separateness from the world. Specifically, “ ‘Sanctification’ is thus the state predetermined by God for believers into which in grace He calls them, and in which they begin their Christian course and so pursue it.”
For Christian writers, the calling part is a given. I used to think it would be easy for me, being an introvert and not having to deal with the outside world per se. But in writing you can’t hide – even from yourself – whether or not you chose to publish in the myriad of ways available now. If God calls you to write, He might call you to write some hard truths.
Whether we chose to use foul non-gratuitous language is not a foundational conduct issue. Grace has to be given here. The real issue is being set apart from the world to write what truth God would have us write.