I do think witchcraft and casting of spells is real. I live in Beaufort SC and up the road from me was once the VooDoo capital of the world Frogmore SC. The head guy was Dr. Buzzard. In his life time people from all over the world, even heads of state traveled to this abomination to have him cast spells. I have seen things happen here. I have a elderly man across the street who has been a Christian his whole life who believes in the power of God protecting him. One day 10 years ago someone he had to evict said they cast a Voodoo spell on him. They had nailed a upside down cross wrapped in
cloth to his fence. He took the cross down and he and his wife said there is no such thing as having spells cast on a person, or witch craft. Well 4 days later he had a triple bypass. He has had heart problems ever since. I think the world is full of energy and just like a church praying to make a sick person to get better, like they tell you in the Bible: This is what I think he should have done with the cross. He should have knocked it down with something and said a prayer over it. Jesus protect me from evil. Evil Satan, demons,spirts and evil persons who mean me and my family harm. Evil actions cast words us by people, and the evil words agaist me and my family that come out of their mouths. Then I would have burnt the object, and probably said the prayer again. I think somewhere along the way a lot of things you should and should not do got lost and if you say some thing like "no this is not real" and do not say a prayer to protect yourself for a specific thing, general prayer will bring general coverage. This is just one creepy thing I have witnessed with my eyes.
We did an entire conference on Christianity and the Paranormal this past June. All the lessons are available by CD at www.ipibooks.com. You might want to check it out. I am very skeptical about the power of such people. I believe they prey on the gullibility and fears of people. Obviously, I do not deny the reality of Satan or of demons. However, biblically, I do not see support for the belief that people practicing Voodoo have any real demonic power. I do not absolutely rule it out, but my first assumption is to be extremely skeptical of these claims. Fear is a very powerful thing and these people use this fear to manipulate people into believing they have real power. I believe that a clear-headed analysis of (or to be a bit more cautious nearly all) such claims that spells worked would show that it is the power of suggestion, of fear and of emotional manipulation which is working, not some sort of supernatural evil power.
I will use the example you gave to support my opinion (for what it is worth). I feel very confident that if the man had been tested before the bogus cross-hanging trick, he would have been shown to already have atherosclerosis. I assume that he was an old man. It seems beyond the possibility of belief that a "spell" could put placque into the coronary arteries of a man. I do not absolutely rule this out, but I believe a much more rational and reasonable view would be that the man was already sick. Might emotional stress brought on by the persecution of these people have made him upset and caused a crisis in the heart condition he already had? This is very possible.
In any case,
I already said that I am extremely skeptical of these claims, but I do NOT rule out absolutely the possibility that Satan could empower some practitioners of satanic arts with real power. I believe it is very unlikely but not impossible. However, one thing I can say with great confidence is that Christians do not need to fear such things. It is not possible for a Christian to be possessed by a demon. The Holy Spirit and a demon cannot occupy the same person. Christians do NOT need to fear voodoo or any other so-called black magic. I agree with your friend that it is silly and really a sign of lack of belief in God to go through some sort of burning ritual. I am not saying that it is would be wrong to pray about such a thing. It is never wrong to pray. However, we should put our faith in God, not in the power of burning a piece of wood which has no power anyway.