Lenore Skenazy made a very good observation there, one that has occurred to me many times before.
You
know your neighbors. Even if only by sight. You know what they are like. You know they aren't poisoners.
They don't attempt to kill your children the other 364 days of the year- why do you think they suddenly turn into murderers on Halloween?

Do you think the spirit of the Great Pumpkin King possesses them and turns them into apple ravor killers?
You don't worry about living down the block from a poisoner and/or child killer about 0.997260274 of the time. Why is the other time any different or special just because there is candy being handed out?
If there
were one living in your neighborhood, you can bet that he/she
wouldn't confine him- or herself to Halloween.
Ah, but you say "Well, of course I'm not worried about Marty from upstairs or Jack and Lindsey down the street or those Indian people next door. I'm worried about the ones I
don't know. I'm worried about anyone out there who might want to do something bad."
Really? Where do you think this faceless shapeless bogeyman phantom comes from? Does he float in through another membrane every October 31st and plop down in a house on your street?