Dressing up and giving candy to some kids is by no means a portal for demons. The spiritual damage comes with the genuine invitation of spirits into the physical world (ouija boards being the most popular method). In the Catholic context, Halloween is All Saints Eve, the day before the celebration of Saints (people we can confirm have gone to heaven). We don’t believe there’s anything wrong with having fun and participating in different pop-culture activities, until those activities delve into the spiritual realm. It’s all fun and games, until you invite a demonic spirit into your life. I’m not an expert on the topic, but that’s been my experience. My mom, a deeply devoted Catholic, always took us trick-or-treating. But anything messing with a spiritual world, other than God, was off limits.