Sure I'll be flamed, but here goes....
When I was the equivalent of Yr 6 back in the late 1970s, teacher read us a story ("The Turbulent Term of Tyke Tyler". I recommend this for your children, it's great!) which led me on to read (by the same author) Gowie Corbie Plays Chicken. In which book, an American girl comes to the UK and introduces Trick or Treat. (which they mis-hear, and think is trickle treat)
That was my first introduction to it. I think my Dsis did it with a friend in the early 80s. Most people were mystified and alarmed.
FF to me having a DD. VERY pfb. NEVER gave her sugar. Warned against strangers. Tried to teach not to be grabby or greedy.
Why then should on one night a year that ALL go out the window and she harrass strangers for foods I don't want her to eat?????
I do have ONE exception to this (and for which if this is your experience, I understand the 
's that'll no doubt come my way).... One year we went out with a friend, in a very small area, where everyone knew everyone, and they ONLY knocked at houses with a light on, and everyone who was knocked at was pleased to give a 'treat'. That was really sweet. The kids enjoyed the dressing up, and didn't want to knock on any doors which didn't have a pumpkin/light.
But generally, I think this is horrible, and goes against everything we teach our kids on every other day of the year, and isn't 'our' tradition in the first place!
Throw those biscuits at me for being a kill-joy! (I do have sweets in already in preparation. I promise I won't rant at children on Monday!)