My 16 year old daughter has a severe peanut allergy. We found out when she was three years old and almost stopped breathing while we were at one of those steak houses where you throw the peanut shells on the floor. She carries an EpiPen everywhere. We never bothered to take her trick or treating, because the vast majority of chocolate candy, even if it doesn't contain peanuts, is manufactured on equipment that also handles peanuts.
We're not psycho parents about this, because we don't want our daughter to be psycho either. We read every label, ask for the allergy guide at restaurants (they all have them), and we've never had a problem. If we think there's going to be an issue, she just brings her own food.
Unfortunately, some of the recent popular sensitivities have softened the general public's opinion of true allergies. Gluten and lactose, to name a few, can certainly make somebody uncomfortable (and in the case of lactose, those around you), but you're not going to die right there.