Speculative fiction—what is it? It's a sub genre that speculates about fictional worlds, realities and times. Is that anti-truth? No, it's fiction. A tool used to tell a story. For example, if an author chooses a time travel theme that allows Hitler to accept Christ and repent of sin, it's an alternate time line that shows the power of Christ. It would be controversial to say the least, but it is still fiction. Committees and religious watch dogs may pick such a story apart to read into it a love for Hitler, hatred of the Jews, or any other thread that ties to that time in history. However, if written well, the story becomes a powerful tool that exposes the truth of the gospel and its ability to change lives. It may even do a work in touching a sensitive need for change in the reader's life.
Christ used fictional scenarios as a tool to reach people with the truth. Consider his parables of the lost coin, the lost sheep or the lost son (just to name a few). He used these fictional stories to stir people to think on a deeper level. (I'm in no way claiming speculative fiction equal to God's word.) Following the parables in Matthew 25, including the lesson of the Sheep and the Goats, the religious leaders planned to find a way to kill Jesus. They didn't care for the message.
To label the tool good or evil is narrow-minded thinking. A knife used to cut the meal on your plate or a knife used to harm a fellow human being is still a knife. Speculative fiction is no different. It's the tool that carries a fictional story.
God creates each person as a unique individual. We have likes and dislikes. Some people like sci-fi, fantasy, mystery, etc. Those who don't care for sci-fi, fantasy and horror cannot understand those who do. For Christians who do, finding Christian speculative Fiction offers a refreshing difference.