You should have a conversation on how to handle that in the future when kids come along. I used to have my kids dress up as something neutral. There has been some discussion lately if Halloween really had a demonic background, but he should respect your opinion regardless. But you should find a solution both are enthusiastic about. If he only says yes to keep the peace, you will have problems later down the road. Many christians would agree with you that such movies are demonic, but many others see them as you would fairy tales. Interesting to look at, but nothing to do with your faith. I used to lean to the former side, but am now somewhat more in the middle. I don't watch them, but my husband and older (past puberty) children do. Although I am not thrilled about it and would rather they read their bibles, it is not enough of a priority for me to make a fuss about. My husband was an atheist when we met, but now goes to church with me.
The two of you should look for a mutually agreeable solution. That could be, that he only watches such a movie when he goes to the cinema with friends, or you go on vacation around halloween. Who knows. It is your marriage. You cannot and should not force him to see things the same as you or question his belief system, as these are also disrespectful judgements, and he should not laugh about your concerns. Even if you thought in the past that he thought the same, you should now be honest with each other and brainstorm long enough over the course of the next few weeks to come to an enthusiastic agreement. Don't discuss this shortly before Halloween.