The holiday goes back, like so many holiday traditons, to pagan celebrations:
Halloween's origins date back to the ancient Celtic festival of Samhain (pronounced sow-in).
The Celts, who lived 2,000 years ago in the area that is now Ireland, the United Kingdom, and northern France, celebrated their new year on November 1. This day marked the end of summer and the harvest and the beginning of the dark, cold winter, a time of year that was often associated with human death. Celts believed that on the night before the new year, the boundary between the worlds of the living and the dead became blurred. On the night of October 31, they celebrated Samhain, when it was believed that the ghosts of the dead returned to earth. In addition to causing trouble and damaging crops, Celts thought that the presence of the otherworldly spirits made it easier for the Druids, or Celtic priests, to make predictions about the future. For a people entirely dependent on the volatile natural world, these prophecies were an important source of comfort and direction during the long, dark winter.
To commemorate the event, Druids built huge sacred bonfires, where the people gathered to burn crops and animals as sacrifices to the Celtic deities.
Like Christmas, the Catholics tried to incorporate non-Christian practices into a religiously respectable form. They decided to use the celebrations as a time to remember Saints and martyrs instead of pagan gods:
By the 800s, the influence of Christianity had spread into Celtic lands. In the seventh century, Pope Boniface IV designated November 1 All Saints' Day, a time to honor saints and martyrs. It is widely believed today that the pope was attempting to replace the Celtic festival of the dead with a related, but church-sanctioned holiday. The celebration was also called All-hallows or All-hallowmas (from Middle English Alholowmesse meaning All Saints' Day) and the night before it, the night of Samhain, began to be called All-hallows Eve and, eventually, Halloween. Even later, in A.D. 1000, the church would make November 2 All Souls' Day, a day to honor the dead. It was celebrated similarly to Samhain, with big bonfires, parades, and dressing up in costumes as saints, angels, and devils. Together, the three celebrations, the eve of All Saints', All Saints', and All Souls', were called Hallowmas. (See The History Channel:The History of Halloween )
Not everyone likes the idea of Halloween, and some refuse to participate. Those who are most concerned are traditionalist Protestant Christians who see the holiday as incompatable to their beliefs. Some even condemn it as a Satanic conspiracy, Harry Potter like, to recruit followers of the occult:
Many . . . Christians . . . consider Halloween as incompatible and even conflicting with the Christian faith, due to its preoccupation with the occult in symbols, masks and costumes, its origin as pagan festival of the dead, and its celebration by satanists. They argue that Halloween is also a prime recruiting season for satanists and therefore poses a considerable harm to children. Others are concerned about vandalism and destructive behavior after a church had become a victim of destructive "shock rituals" by satanists leading to targeted monitoring of these gatherings by the police. Another argument brought forward is that according to occult Wicca practices “Halloween is one of the four major Sabbats celebrated by the modern Witch, and it is by far the most popular and important of the eight that are observed. . . Witches regard Halloween as their New Year’s Eve, celebrating it with sacred rituals. . . (Dunwich, Gerina. The Pagan Book of Halloween, p. 120). The opinion which rejects Halloween because it trivialises the realities of 'evil' and 'the occult’ is shared by some Christians across all denominations. Some Evangelical and Protestant Churches, and some Jews and Muslims, strongly object to the tradition and refuse to allow their children to participate, pointing out to its pagan origins as well as what they consider its satanic imagery.(see Halloween from Wikipedia )
For the most part, Mormons haven't had any opinions of it as a group. There are, however, differences of approach. For many Latter-day Saints the season continues to be about having fun with their children. They get them dressed up and go visit family and neighbors who give them candy and otherwise enjoy themselves. Over the years there has been a development that, although not unique, does seem to have caught hold almost as a Church wide tradition. Trunk or Treat might not have been started by Mormons, but it has definantly been adopted by Latter-day Saints as their own special tradition. Considering the breakdown of neighborhood safety and the strong beliefs about community in the faith, it shouldn't be surprising. It is a way to have both safety and still retain the sense of community. In some ways Halloween has become a sweet tooth communion of family and friends.
Other Latter-day Saints, perhaps a small minority or silent majority, are more critical of the seasons implications. The more vocal individuals condemn it for much the same reasons as others who are not of the same faith. The biggest reason is not fear of pagan influence or satanic recruitment. It is more about allowing evil and wickedness a time to be celebrated. The less vocal Latter-day Saints who object to the holiday simply don't like the blood, fear, and lack of a spiritual enlightenment. They see no reason to have it, and a few reasons to reject it.
That brings it back to myself. You might say that my house is split on the subject. I love to get dressed up, watch spooky (not bloody) shows, and generally eat lots of candy. My wife, on the other hand, simply doesn't want to get involved. She has no problem passing out and eating candy. It's the rest of it she doesn't like. I imagine this isn't an unusual situtation.