Do not see where there would be any conflict.
I'm a Christian, but writing (erotica or otherwise) makes me happy. God gave us all free will to live our lives as we see fit. Until God tells me writing erotica is wrong then I'll stop.
You can still be a christian and enjoy not only writing about sex but enjoying it as well.
I am well aware of many regular church goers who participate in the joy of sex. I was one as a teen and after Sunday night service - well lets say it was orgasmic..
I have read the posts on this thread with interest. I know from other Forum posts that many of those who have posted here are active Christians, as I am, who find no problems with reading and writing erotica, and sharing their fantasies with others - including cyber sex. Personally I have said much of what I believe elsewhere, on the thread "I Am An Atheist. (Does that offend you?)", but I will repeat here that I am an active lay preacher in the UK Methodist Church (a Deacon to those of you in the USA), but find no conflict between my membership and enjoyment of Lush and my faith.
There are things about me that I think are sinful - a list might include:-
Sex trafficking
Grooming of underage girls for sex (read about recent events in Rochdale, UK)
The buying and selling of people
Forcing others into degrading behaviour
Physical and sexual abuse of others
Enslavement
Pursuit of unjust policies by those in positions of power
Political acts that increase the inequality in the world between rich and poor
Exploitation of the poor by the rich
Oppression of poor peoples
Oppression of women by men
Torture
Sale of arms to developing countries
I could go on, but my list says far more about such things as exploitation and injustice than about sex. Sex was controlled in the past by societies to control their fertility - this was important to ensure their survival in a difficult and hostile world. However, from very early times control of sexuality has been of the power game between men and women, more specifically the way in which men have tried to control and restrict women's freedoms - this is still seen today in the beliefs of the Taliban, which have nothing to do with Islam.
The Church has been guilty of this for much of its 2,000 year history, downplaying the role of women in the early church (they were the first witnesses to the Resurrection, but the men didn't believe them), and going as far as to make the nature of God wholly male, whereas in Jewish Wisdom literature, the Spirit/Wisdom of God was seen as female working with God in Creation from the beginning of things. This male centric view, coupled with a Jewish distaste on the part of St Paul for the more relaxed attitudes to sexuality seen in the Greek world, is what has led to the negation of sexual pleasure that has so often been preached, along with a view that women are basically sinful and therefore not fit to hold office, let alone priestly office. The Old Testament prophets railed, not against sex, but against unjust rulers who exploited and oppressed the people in their care, and when they spoke about adultery it was in terms of a people who had turned away from their God (Yahweh) to other Gods such as Baal, and even prostitution was used as an allegory for the failure of the relationship between people and God.
People are made in the image of God, a God whose love and grace was so great that he was prepared to give up all power and become incarnated in humanity and to die the death of a criminal terrorist because of the way his preaching and teaching challenged the hypocrisy and evil of those in positions of power and authority. The Resurrection is a mystery, whether it was physical, or only spiritual, but is at heart a profound demonstration that love and good will alway eventually triumph over darkness and evil.
To judge what is sinful for oneself means firstly to align yourself with God's will which is for peace, truth, justice and love to prevail throughout the world. And if you are afraid of judgement, just think for a moment that God might be rather more concerned with the actions of our leaders, who continuer to exploit and use others for their own ends, than your enjoyment of innocent sexual pleasure through reading and writing erotica, and sharing your fantasies with other like minded and liberated people. As someone else said much more simply than me, God invented sex as well as gender for the enjoyment and fulfilment of people just as much as for procreation, perhaps much more so.
As a Christian myself i have thought and struggled with this for a long time. I am hoping this ends up making some sense. I believe that masturbation itself is not wrong. There is nothing i can find in the bible that says masturbation is wrong. The bible does say however that lusting after someone in your heart equates to adultery and therefore sin. But in stories there is no picture of or person that you are lusting after so that seems fine. I myself would only be able to write stories where the two characters were married or got married. Got married as in they have sex out of wedlock but then get married to that same person. In the bible the definition of marriage in genesis with adam and eve was that once you have sex you are now married. Or one flesh as the bible calls it. Whereas i couldnt write stories about men who have sex with multiple women cause then it is something i know is wrong. I hope that made at least a little bit of sense.
I just really don't think it could work honestly. Those two things are just too different, somehow you'll always be breaking some rule, which is a sin.