Why is there Halloween?
A different explanation.

Halloween? Isn't it Satanic? the old Black woman chided me on the bus. We often talk about cultural matters.
"Actually, it's as Christian as, well, Corpus Christi."I said. Being observant Anglican has some advantages.
"Well it's not in the Bible."
"No, but it's not pagan, either. Why do you think it's on the eve of All Saints? And what about All Souls Day? 'Let us now praise famous men..?'"
"All Saints is Satanic. All Souls is Satanic, a man-made holiday!"

Resisting mightily my urge to put on my lapsed-Satanist pointy hat, or Secular Humanist hat (I doffed them both rather publicly, a few years ago), and point out that the Bible is also a human artifact, I reminded myself of my favorite explanation for Halloween, which is completely non-Satanic, non-Fluffy Wiccan, and only faintly partaking of witchcraft As We Know it...

It's to be remembered that while many of its neighbors were pagan, Ireland remained a Christian entity, separate from Rome for several centuries, resulting, in some cases, in an odd hybrid of practices. For instance, the end of the Irish Civil Year was when the last sheaf of grain was harvested, and began on All Saint's Day. Most years, it was fairly close, even overlapping, so that there was little ambiguity. However, some years, grain had to be harvested early, and so there might be anything from a night to a week that belonged neither to one year or another.
This kind of calendrical glitch was not uncommon in some societies -- in Early Rome, there was no reckoning of days or months between December and March. In Ireland, however, this situation led to a mild social crisis every time it occurred.
It was hard to press any kind of civil suit that occurred on no particular day of no particular year. It was easy to get away with all kinds of petty crime, quasi-legal mischief (like fortunetelling, spellcasting and begging) and revenge pranks, too. Therefore, especially at night, people stayed home, lit candles in apples and turnips and left them by the door or in a window, and if they had to go out, they'd cover their faces, turn their clothing inside out, or do other things to disguise themselves.

Shut up for long nights and short days, people began to wonder: if it's no real year, did that mean there was no time? Would that mean that places, events, even people from the past might, somehow, be walking around out there? All Saint's was the day for the commemoration of holy people. All Souls was for the ordinary kind of person, the souls in Purgatory. The Eve of All Hallows must, therefore be when those in Hell might walk free! The English invaded, the Irish Civil calendar was discarded, but the idea of late October as a time of fear and mischief remained.

And so it was, that in Early America, Irish young men would go forth on the last two nights of October, wreaking havoc (overturning outhouses and/or lighting fires was a popular gesture), getting drunk, and generally being a public nuisance until the 1930's when the Boy Scouts got into the action, substituting doing skits, songs and magic tricks in costume for the "trick" part and encouraging grown folks to "treat" them with candies, hot cider, doughnuts and the like. In the 60's UNICEF used the idea to collect for children's charities, a hard sell for smaller kids to'get', but amazingly effective. Nowadays, the only people truly frightened are parents, who love outdoing each other on how terrible it all is.

It may be not everyone's explanation, but I'm sticking to it.