umm actually it has nothing to do with dressing up scary.....
" It is thought to have originated with the ancient Celtic festival of Samhain, when people would light bonfires and wear costumes to ward off roaming ghosts. In the eighth century, Pope Gregory III designated November 1 as a time to honor all saints and martyrs; the holiday, All Saints’ Day, incorporated some of the traditions of Samhain. The evening before was known as All Hallows’ Eve and later Halloween. Over time, Halloween evolved into a secular, community-based event characterized by child-friendly activities such as trick-or-treating. "
so you wear costumes to ward off roaming ghosts... it has nothing to do with being scary... its jsut that scary stuff is so much cooler