I don't understand the relevance. The scripture you quoted refers to offerings to other gods. In this case, we're talking about books and movies that don't have anything to do with gods or Christianity.
I guess I don't understand what "issue" we're talking about. Is the argument that someone who's weak in their faith will read a Harry Potter book and be like, "Well, I'm not a Christian anymore"?
I will do my best to explain my thoughts! I always don't reflect my thoughts in mind with appropriate words.. So apologies if I end up confusing you more Paul was writing this to the prevalent culture at that time.. I come from India and I exactly know what he is talking about.. Hindus offer food to idols before eating.. Now if there is a convert from Hindu, obviously it would be in his mind that it is absolutely wrong.. The reasons could be different.. He might think he would become demon possessed by eating the food.. Many people in India still believe Christians will fall sick if we eat food offered to idols. Even my Indian church pastor believes in that I sort of argued with him.. Now, is it appropriate for me to deliberately eat sacrificed food in front of such Christians? Because I am matured enough to know that it is just going to come out the other side? That is what Paul is saying..
Taking this to today's culture.. Watching Harry Potter movies.. Create an opinion poll among Christians.. Ask how many people believe they could be influenced by demons by watching Harry Potter movies.. I am sure you will get overwhelming response.. They are not to blamed as they are not mature in the Christian faith.. And they don't look at it from legalistic perspective.. It's just something that would be in the conscious.. Instead of causing more confusion to their conscious, let's not just watch the movies! Since we are talking about a social issue, when a group of Christians endorse Harry Potter movies, it throws confusion for less mature Christians.. That is why I am saying, as more mature Christians let's not do anything which is not going to glorify God.. I am not saying watching Harry Potter movies makes us any less Christian.. but it does not strengthen the fellowship.. That is all I am saying..