But I thought the point of dressing up in scary supernatural-themed costumes, on the day before All Saints Day, was partly to lampoon evil. “Ha ha, you’re so week compared to almighty God and his Saints!”
I grant you, some people actually DO celebrate evil (in which case I would agree with Mr. Costume Police), but I think the great majority just “laugh at the devil” and that such is harmless, even salutary.
The Celts believed that during Samhain the wall between the living and dead got so thin the dead could come through. People wore scary costumes so the harmful spirits wouldn't notice them. The practice was later absorbed into the Christian event placed around the same time. I say around because Samhain (and thus Halloween) goes according to the Celtic lunar calendar, so would be on the new moon around Oct 31, which is Nov 6 this year.