Answers are going to vary by perceptions and by authors intents.
I view it as you can be a Christian writer, or you can be a Christian who writes. To me a Christian writer is someone who specifically writes to encourage/entertain/teach other Christians or to spread the truth as they see it to unbelievers. A Christian who writes may or may not do that, and could write about anything that includes something Scriptural or about Christian life or not.
Regardless of what kind of writing we do, as Christians we are representing Christ, no matter what we do. So our behavior, attitudes, and choices should reflect that. What does that mean in specifics? That's something that the individuals need to come to terms with between themselves and God.
I write a lot of children's stuff (and have a hybrid deal in the works!!!!

) but I also like Chick Lit and creative non-fiction. I have a few works in progress that toe the edge, and I'm wondering how far over the edge should it go? What would an audience think? If my intent is to draw in people who might have a hard life and not be aware of the love and compassion of Christ, do I care what the sensitive Christian crowd that has it all together thinks? Is unnecessary violence or sexual content going to promote the message or hinder it? How much do
I WANT to think about the bad things?
It's important to ponder these things, search Scripture about how to imitate Christ, and follow the convictions from the Holy Spirit.