I decided to take a peek at the history. It's long and complex, and it appears that it in fact started out as a Christian holiday, and perhaps even a Jewish holiday. I'm sure this may be horrifying to my atheist and secularist friends who suit up for the occasion. Things have the meaning we give them though, so apply what you will.
It appears the holiday was created by the Eastern Church in the 4th century to commemorate “All Martyr’s Day,” and was observed in May. Rome used to slaughter Christians, so the day was primarily in remembrance of them. Eventually people started having pageants and parties, and came dressed up as their favorite martyr. Others came dressed as Satan, Romans, wild animals used in the games that killed Christians, and other opponents of Christianity.
Over time that day became known as "All Saints Day". At the time Christians' and Jews' holy days began at dusk, so the evening before was “Hallowed Even’, much like Christmas Eve. That was shortened to “Hallowe’en”. So on the eve of the hallowed day, Christians went door to door to collect for the poor. Now kids (does this still go on?) go door to door for candy. Instead of "trick or treat" there was a chant, "Soul, soul! for a soul cake! I pray, good mistress, for a soul cake! An apple or pear, or plum or a cherry. Any good thing to make us merry. One for Peter, two for Paul, Three for Him who made us all. Up with the kettle, down with the pan. Give us good alms and we’ll be gone."
The Jewish linkage is the Festival of Purim, celebrating Ester's saving her people from a horrible holocaust. The slaughter was to take place in the spring, on the 14th day of the Hebrew month Adar. God, through Ester, stopped it, and that day became a day of celebration. Those two days, the eve of, and the day of, are Purim, a celebration. Book of Ester: "...as on which the Jews had rest from their enemies, as the month which was turned from sorrow to joy for them, and from mourning to a holiday; that they should make them days of feasting and joy, of sending presents to one another and gifts to the poor." The kids dress up in costumes of Jewish heroes and the persecutors of Jews, have baskets that they take to homes of others, and are given treats in return. I apologize to my Jewish friends if I don't have this exactly correct.
I think there's plenty here for both religious people and secularists. There are plenty of pagan connections too. Give it the meaning you want. Let kids have their fun. I will protest of course, adults using the evening to destroy things, celebrate evil, pain, torture, and bloodletting. I'll protest too parents that let their little girls dress up like sluts, street prostitutes and whores. I just now thought, what would happen if some kids went as priest or nun to school on Halloween instead of Satan or pimp or whore or ax murderer?