It's not of pagan origin.
Well October 31st is a Pagan holiday called, Samhain. Its the Celtic New Year, which is also when the Fae would rise from the ground to dance and ensnare men and women and children into coming with them back to the realm of the Tuatha.
Hallowe'en, or All Hallow's Eve is part of the liturgical calendar of Catholicism. It is the day when we (meaning Catholics) are supposed take stock of the glories of God and all those who passed in the last year and to pray for all the holy souls in purgatory (
Not looking for an argument, telling you the origin). The next day is All Saints Day, a celebration of those who have entered into Heaven and all the holy angels in Heaven.
The modern traditions of Halloween actually come from three sources:
Pagan
Masks, Jack'o'Lanterns, going door to door.
Catholic
Celebration of those who have passed on, going to friends or relatives houses
Commercial
CANDY!!!! CANDY!!! CANDY!! CANDY!
By the way, by the time period that Samhain (pronounced Sow-win) was celebrated, the Druids of Ireland and Northern Scotland had fully rejected human sacrifice. No sacrifices were to be performed on Samhain. Instead, it was a time of family enjoying the first fruits of the harvest, and staying the hell inside because the Fairies would take them away if they noticed a human outside (hence the Masks part of tradition. If you had to go outside, you put on a mask that would obscure your face and cause the fairies to think you were one of them.)