Dressing up, playing pretend, was something we did every day as children, so Halloween was really not that different from any other day, pillowcases full of candy notwithstanding. In my imagination, I was Lucy shivering in the cold after exiting the wardrobe for the first time, I was Pippi climbing a tree and breaking all the rules a good girl usually followed. Other days I was Nancy solving a mystery, or a Jedi knight using the force, or Spiderman swinging from skyscraper to skyscraper on a silken web that I shot out of my wrist. I was all the things I would never be in real life.
As adults, we no longer get to play pretend, or when we do, it is deemed somehow subversive (furries and drag queens and sexual role playing, for example). But for one night a year, the venerated All Hallow's Eve, we are allowed to indulge our fantasies and it is considered, in this era of ever-increasing restrictions and considerations, socially acceptable to take on the identity of something you are not.
I am something of a Halloween purist, in the sense that I believe Halloween costumes should be scary, should be worn to ward off the dead spirits that break their supernatural bonds and walk the night, shambling, slinking, stalking, seeking their earthly prey. I do, however, understand the desire to cast aside the identities we are shackled to in our daily existence and become something greater, something dangerous or wild or provocative, something other.
There is something attractive about otherness, but there is also something inherently dangerous about it. The biological strategy of making generalizations developed as a way of helping us determine our safety (little cat-mostly safe, really big cat-dangerous). This biological tendency to differentiate and categorize works mostly to protect us. Historically it was important that I recognize someone's otherness because if he wasn't related to me, maybe he was going to beat me up and kill my offspring and steal my food. We were all just fighting to survive.
We no longer need this sort of protection in today's global and "civilized" society, of course, but there it is, hardwired into our DNA. Perhaps the prevalence of costumes that perpetuate cultural stereotypes is not so much a reflection of an individual's inherent racism as it is the desire to become, for one night, something completely foreign, to adopt the identity of an other in order to face our fear of it. We cannot truly understand what it feels like to be in another person's skin, of course, any more than I could have shot those silken strands out of my wrists and swung through the night sky. But I'm not sure that the desire is as malicious or ignorant as some suggest.
This desire also explains the preponderance of so-called "slutty" costumes. (This works both gender ways: men aren't generally encouraged to walk around in loincloths, but Tarzan remains a popular costume.) Who among us does not want to feel sexy and desired? But how many of us are allowed to explore that aspect of our human animal in public? Undergarments should be hidden and our sexual urges should be restrained, or at least relegated to the bedroom, preferably with one monogamous partner. The French maid, the sexy nurse: there is nothing sexy about dusting or changing bedpans. The sexy comes in the subservience. Halloween gives us the opportunity to appear (and possibly behave) in a sexual manner that is typically frowned upon in public settings.
At its historical base, Halloween is about faking an identity to trick the ghouls who want to steal our souls and drag us with them into the underworld. As adults, the concept of mortality becomes less than abstract, so this taking on of new identities, of playing pretend, becomes an important annual escape from the scary things in life: the darkness of the other, the darkness of sex, the darkness of death.
Obviously, not every costume needs to be fraught with deeper meaning. Some costumes are crafty or witty or topical or cute. Halloween is also an escape from the solemnity of life. It is an inversion of the natural order of things. It is a time when entry-level retail workers can become dominatrixes, when boys can become girls and girls can become boys, when middle-aged men and women can become superheroes and middle-class girls (and boys) can become princesses.