Back in the 1970's right after the release of the first Star Wars movie, I was in a Christian bookstore. On the shelf I saw two books one identified all sorts of Christian imagery in the movie and used it as a tool for evangelism. The other denounced the movie for drawing from Eastern Mysticism and condemned it as demonic. About the same time I saw the same types of interpretations of Jonathan Livingstone Seagull.
Speculative fiction will elicit different responses in different people. Of course, that is true of any type of fiction. What one person can read without problem will disturb another person deeply. Unfortunately, there isn't a simple answer to the question of whether Christians should be reading speculative fiction. It depends largely on the individual Christian.
But this isn't new. Back in the days of the Apostle Paul, it wasn't speculative fiction, but eating meat. You see, butchers in Rome would process their meat under the gaze of an idol of a state sanctioned God. They were required to do so. Jewish law said that one was not to eat meat offered to idols. Of course, there is a difference between slaughtering your own bull and then in devotion to that God offering the meat to the idol before eating and simply buying beef that happened to be sitting on a table in front of an idol that probably even the butcher didn't revere.
Nevertheless, a dispute arose among the Roman Christians. One side said that it was meat offered to idols. That settled matters. Don't eat it. Others said that God sanctified the meat if it was eaten in faith and that it was foolish of the other people being so squeamish.
Paul's response found in Romans 14 shows how to handle controversies over things not clearly defined in scripture as sin.
He says that some people are strong in the faith and can eat of the meat without feeling condemned. If that is the case, then it is not a sin to them. However, others not so strong would feel condemned and their eating would not be in faith. Therefore, they should not eat.
Here's how Paul put it:
And receive him who is weak in the faith, but not to judgments of your thoughts. For indeed one believes to eat all things; but being weak, another eats vegetables. Do not let him who eats despise him who does not eat; and do not let him who does not eat judge him who eats, for God has received him. Who are you that judges another's servant? To his own master he stands or falls. But he will stand, for God is able to make him stand.
For "eating all things" insert "reading speculative fiction" and we have a guide for dealing with critics. We are not to judge them. I know, that is hard to do when they may be judging us. But I can't control anyone else, but myself. We should not consider them narrow minded or stupid if they can't watch a Harry Potter film or conceive of Christian Fantasy, Horror or Science Fiction. They are following their own conscience as they should. Paul puts it this way:
So then let us pursue the things of peace, and the things for building up one another. Do not undo the work of God for food. Truly, all things indeed are clean, but it is bad to the man eating because of a stumbling-block. It is good neither to eat flesh, nor to drink wine, nor anything by which your brother stumbles, or is offended, or is made weak. Do you have faith? Have it to yourself before God. Blessed is he who does not condemn himself in what he approves. But, the one doubting, if he eats, he has been condemned, because it is not of faith; and all that is not of faith is sin. (Rom 14:19-23)
So, now we come to the question of how to respond to our critics. The answer is "to pursue peace." In other words, speculative fiction isn't important enough to tear down the work of God being done through our relationships with others. That doesn't mean you go through your house and throw out your science fiction, fantasy and horror books because you have a friend who doesn't believe in such things. But it may mean that you don't leave them laying on the coffee table when they come to visit.
Some people because of their personal histories, might not be able to read speculative fiction without their relationship with God being affected. For instance, someone who has come out of the occult, might be tempted back into that lifestyle reading even Christian stories dealing with such topics. Others may simply have personal convictions based on teachings they have received that such things are wrong. So, we need to respect those feelings.
Likewise, though, they need to respect ours. So, if they will not let up, we can say simply, "The Bible says we are to pursue the things of peace. I know you have concern for me. And I appreciate that. However, I don't consider speculative fiction to be endangering my relationship with God. If it does, I trust God to show me that. I know your opinions on this. You know mine. Anything further would probably just lead us both into saying things we might regret. So, let's just talk about the things we share in Christ, and let him take care of the rest."
Remember, to follow the law of love and gentleness of spirit when asking for their ceasing to criticize you. And if you respect their feelings without sharing them, very often they will reciprocate. But even if they don't. We still have no right to be harsh with them.
We don't need to make converts to speculative fiction. And I, for one, don't want to tempt someone for whom reading speculative fiction could be a stumbling block.