I've heard of some of the more extreme claims of these witch doctors. Those I've heard of tend to be called VooDoo though.
Some people seek hope in seemingly hopeless situations. The material promises of these charlitans can seem to offer that hope. Other simply seek an edge.
There have been a number of reports of particularly nasty things happening as a result of these people. But we should aways be aware that they and those that listen to them are in the minority.
We should also be aware that such stories, about Africa, tend to be lapped up by some press outlets and their readers.