Perhaps I'm wrong, but yes what you say applies to All Saints Day, but I'm talking of All Saints Day Eve, which is supposed to have it's own significance, if allowing for Celtic tradition to mix with the Catholic holiday - going back to the origins of marrying pagan holidays to Christian ones in order to more easily convert the pagans to Christianity. But I am not a religious historian of any kind, but my exposure has always alluded to this being truthful.
Originally, Halloween, as practiced by pagans was called Samhain (pronounced sow-when, probably a celtic or gaelic word). One aspect of the holiday (like Thanksgiving) is as a Fall Festival, celebrating the bounty of the harvest, etc.
When Christianity was spread, as GP indicates, they'd merge/replace the old holidays with Christian versions. Easter is like that, as it was formerly called Ostara and was a fertility holiday (hence the bunnies).
And as with most spiritual things, there was meaning associated to the opposite/reverse. So if there's All Hallows Day, there is All Hallows Eve (the day before).
Per the History Channel, Halloween varied in its significance to various cultures. It wasn't until the 20th century when the concept of dressing in costumes and going trick or treating evolved. There was no religious association with the trick or treating idea, it was just a party/activity concept that evolved.
Ironically enough, knowing this history (having seen the Hitler Channel, knowing pagans, etc), there have been some religious groups in America who thought Trick or Treating was the pagan activity and "wrong" So they've started having Fall Festivals on their church grounds for Halloween events. This is ironic, because Fall Festival is in fact the original purpose of Samhain in early pagan culture. So they are in fact shunning the very American non-pagan practice and adopting the pagan practice under the objective of avoiding a pagan practice.
Note, this is only intended as information and not a discussion on the merits of any given religion. I cite the anti-halloween example to reflect how a few groups' ignorance about the holiday has unwittingly driven them back to the practice they allegedly sought to avoid under their declared reasoning for doing so. There is nothing wrong with their chosen way to celebrate the holiday, but doing so under mistaken understanding of history is a darn shame.