Are there red lines in writing?
Can I make the devil good, just for fun.
Could I use the means of Darkness to represent the Light?
And is artistic writing at all subject to responsibility, because it is fiction?
P.S. I am not an extreme puritan, but a brother of mine agreed to translate a horror opera and I think it did not reflect well on him. He does not think it is a problem, but I worry about him.
From a Christian perspective, the Bible does talk about setting no wicked thing before your eyes, thinking on good things rather than bad, etc. If you are writing it, then not only are you looking at it and thinking about it, but you are making it up for someone else to see and think about.
As for red lines, I think there is some room for personal conviction on what is acceptable and not, but I think many writers (even Christian) put way too much emphasis on dark stories. While I do occasionally write stories that show the darkness and even despair, I always tried to conclude with a message of hope and redemption. I think that is very important to do as a Christian writer.
There are some things are simply violate the natural laws of existence as was stated before.
However, in answer to your question about the devil being good, you could go with the idea that he was once a perfect angel in God’s presence before he fell. So you could show how God created everything perfect but pride destroyed it. However, the Bible also says that angels can not be redeemed once they turn away.
But yes, I do believe that fiction is very important and should be treated with care.