I don't celebrate Halloween. The most I do is carve a pumpkin with my son. That's clean fun. Also, pumpkin seeds roasted with butter and salt is a delicious treat. I give sweets to my students. I'm aware that as I live in Asia I am very far away from the Halloween heartland. In general you don't see the Halloween-themed excesses here.
I will not have anything to do with the creepy stuff. Halloween used to be a lot more innocent. It's getting worse. I don't understand all these adults getting so involved. Weird. They need to grow up.
The best reason I can think of not to celebrate Halloween is that it might offend a Christian brother. The next best reason is the increasing creepiness and weirdness of the event. Having no participation in the day can indeed be a way to witness to one's neighbours. It really depends on circumstances.
But, still, I think it's helpful to distinguish the different sides of Halloween. First of all, what we today call Halloween is not pagan in origin. If it were, it would be clearly problematic for Christians. But the histotical fact is that it's not pagan, and as such the matter is less clear cut than many would like it to be.
There is an innocent side to Halloween, and there is a darker side. It's the grown-ups making it weird.
Repudiating Halloween need not mean that we throw it all out. Pumpkin carving and candy, I think, is fine. If kids want to dress up as superheroes, sure. Keep it clean and fun.