Before I abandoned religion
(decided it was an uneccessary encumbrance to spiritual development),
I did explore the concepts held in various religions.
One of them was Paganism. Haloween is the festival of Samhain
Halloween: The Pagan Festival of Samhain
The practice of dressing up as witches and ghouls is offensive to pagans.
The people who adhere to any religion require it be shown respect.