Most witch-doctors of neo-Pagan, Syncretistic or African cults (as well as those who practive future telling) are fraudulent. However, this kind of evil does exist and some of them truly use demonic power in order to harm or inflict damage on others.
Since most Coptic priests are not native to their home-countries, many of them are not aware of how these practices (Voodoo, Santeria, Palo, Candomble, etc.) take place. It is for this reason that the Church should instruct their clergy about these practices and their origin, since the time will come where many in your congregations will be converts from other backgrounds.
Most of these syncretistic religions originated in Africa as anamist and naturalistic faiths. In the beggining, these practices weren't used as a way to harm others. However, since the times of slavery, Africans used them as a way to defend themselves from their brutal overseers and as a way to remain attached to their African homelands and tribes. The reason why these religions did not fade away was that the Spanish conquerors did not work too hard on the Evangelization of the slaves. While they were very worried about having the Natives evangelized and often punished Indians who refused to accomodate to the new religion, it was enough for them to see the Affricans leaving their idols and using Christian saints as images (after all, they were slaves and their good performance as workers was more important than their devotion to a religion). This meant that most Africans in the Caribbean replaced their idols with Christian statues while preserving their original religion (every statue "represents" a demon and not the Christian saint depicted on it).
The common pattern shared by every African-inspired cult, is the belief in a Creator, a good God who made all things (often identified as the God of Christianity). However, unlike the God of Christianity, this Creator did not remain active and delegated his powers to spirits of nature. It is through these spirits that African cultures attempted to reach the supernatural world in their own primitive environment. However, we must state that the description of these spirits is different from that of Christianity and much closer to our definition of "demon": these intelligent beings have to be served and not only prayed: they demand blood sacrifice and can do both good or evil. Each orisha (santeria) or loa (voodoo), represent the lowests sins, pasions, needs and instincts of mankind (death, violence, sex, alcoholism and reveange).
In fact, every Christian should understand that these religions are actually demonic cults and not simple forms of animism. The Old Testament shows examples about former Pagan cults that strongly ressemble these African religions and their bloody practices: the gods described in the Old Testament were tribal (national) deities just like the African ones. The New Testament also teaches how some people became posessed by creatures named demons and how these demons hace a strong preference for all what is dirty and repulsive. Animal sacrifice is also a common practice shared by all these religious cults, it's in fact a direct rejection of the attonement made by Jesus Christ for the sins of humanity and exposes the hatred of these cults against God' creation.