Oh dear, this will really get me in trouble, but for your sake I will try to explain.
Halloween is, indeed, 'All Hallows Eve' and, as such, is to do with the saints who have died in Christ and will be resurrected when he comes.
However, Halloween is also part of the witches' festivals, which happen every year around the solstices and equinoxes. Which came first, I do not know, but I suspect that the Church wanted to 'christianise' what was a pagan festival.
By celebrating Halloween, which side do you think a casual observer will think you are on? Does witches hats and broomsticks, ghoulish faces and costumes and 'trick-a-treating', etc., and generally looking like 'the undead' strike you in any way as wholesome?
As Christians, we are supposed to identify with Christ and line up with how he feels about things, but if you take part in Halloween, which side do you think you are lining up with? Why not take a vote on it : God or satan, Christianity or witchcraft?
Does making little kids look gruesome, running round the streets threating to throw eggs or flour bags at your door, etc., if you don't give a 'treat' have any relation to Christ? Is it not more worthy of 'the other side'? How can you be so deceived?
I grant you, there is a lot of fun to be had when these 'celebrations' are properly organised and everybody likes to dress up but, as a Christian, I prefer to keep out of it and I warn people that this is not as harmless as it seems.
As the Conservatives in England once said about their policies and those of the Labour, there was the need to put 'a lot of blue water' between the two. Otherwise, people could be excused not knowing the difference.