ProfessorDavey,
Have you ever experienced the paranormal?
No
Have you seen what the evil spirits of this world can do to some people?
No - I've seen awful things happening in this world but they are caused by people, or due to natural phenomena, not evil spirits for the simple reason that evil spirits don't exist.
We never celebrated in this country the USA traditions for Halloween.
Wrong - see earlier discussions - traditions basically identical to trick or treat existed in Britain well before they did in America, albeit called something different. Likewise carving of fruit/veg and 'jack-o-laterns', albeit different type of fruit.
Harmless... is it harmless if your child has nightmares.
My son at the age of 2 had no use for nappies and dry nights. At the age of 4 years he would run to answer the door if anyone knocked. Something we were trying to stop him doing. He had no problem going to get on his bed if tired night or day for a nap.
He was a happy go lucky child. Then one halloween there was a knock at the door and my son was coming down stairs the hall adjacent to the lounge. I got up to answer the door and he ran to it opened it and the look of horror on his young face as he fell backwards off his face stuck in my mind. My son was in shock I looked out to give whoever it was a piece of my mind and there was no one there. All he could say was they had yellow eyes and fangs and long claws. My son had nightmares for months and even wet the bed. He would not go up stairs alone and would not sleep in a room alone.
Halloween, isn't harmless to children? It can psychologically torment and harm a child when (what I assume was an adult )does such stupid things where a child is involved. It took a long time for him to overcome the scare he had. It scarred him for life and he had never liked Halloween since because even today he will tell you it looked so real in his little mind.
I am sorry to hear about your story, and I'm certainly not going to deny its veracity, but I think this is very, very rare. I've never known a kid to be genuinely scared by modern Halloween traditions sufficient to cause nightmares etc. Indeed I think the current traditions of pumpkin carving and trick or treat are so sanitised that there is virtually nothing scary about them. I've known kids scared of all sorts of things - fireworks, clowns, animals, religious symbols etc, but not current Halloween. Should we ban all those other things that are much more likely to terrify kids?
On the latter, despite never having known a kid to be genuinely scared of Halloween customs, I have known I few who were scared and deeply disturbed by Christian symbolism - specifically the man nailed to a piece of wood, 'dying for us'. Additionally the notion of drinking blood and eating flesh, often imposed on children at the very tender age of 7. That is disturbing to kids, not getting dressed as a witch and getting chocolate from your neighbours.
What happens if the door they knock on is a pervert? A peado who then targets those children?
Evidence please of that ever happening. Plus of course there remains parental responsibility. Young kids shouldn't be trick or treating on their own, but with supervision from an adult or much older children.
But on the topic of perverts etc, I'm not aware of Halloween being used to groom children. There are, of course countless examples of children being groomed through interactions with religious organisations.
But even then what really does bandying things about like ghosts and ghouls actually do for children?
In its current form loads of fun.
But if they want to have an Halloween party safely why not. Too many children allowed out alone with parental supervision.
But I believe the world can be harmful and ugly enough without adding our own frightening things to it. 
See above my point about parental supervision.
On the world being frightening - yup you are right it can be at times, and kids actually do need to learn to cope with this. But if you think that Halloween customs are significantly adding to that then you really have completely lost perspective.
