An atheist talkshow host and 12 "like-minded people" are attempting to tackle superstition, mysticism and witchcraft in Uganda. James "Fat Boy" Onen is an on-air presenter for Sanyu FM and a co-founder of Freethought Kampala. Through Facebook campaigns, newspaper articles and regular monthly meetings, Onen believes Freethought Kampala is providing the only rational platform for tackling superstition in Uganda.

This month, Onen has been speaking at events around the UK after being invited by the British Humanist Association (BHA). Addressing small gatherings, he said everyday Ugandans were over-reliant on a "mixed bag" of belief in black magic and Pentecostal Christianity.

"On my talkshow, I offer two million Ugandan shillings to anyone that would prove to me that witchcraft works," he told an audience at the Camden Head pub in London this week. "After three months, one person came forward and took me to a witch doctor, of course he could not do anything." He continued: "But that was not sufficient to change people's minds because they are of the view that evil spirits exist. This is because their pastors are telling them every day that Uganda is cursed and that Uganda suffers from a 'generational curse'."

He told a story of how a Ugandan primary school was shut down because "demons had possessed the children and the management couldn't keep the children under control". Pastors were called but to no avail, explained Onen, who says the children demonstrated symptoms of mass hysteria. This story was not a one-off and was all too common, he said. Meanwhile, Aids victims die because their spiritual leaders advise them not to take antiretroviral drugs (ARVs), he claimed. On top of this, Uganda lives under the shadow of the proposed anti-gay bill, which suggests the death penalty in some cases.

Onen "came out" as an atheist in 2008 after a spate of reports on child sacrifice. He said reading all the "bullshit" about superstition and witchcraft in the press made him co-found Freethought Kampala. "I decided that enough was enough. I and some like-minded individuals decided that we should get together to make a rational viewpoint part of the national conversation."

Before Christianity grew exponentially in Africa, most adhered to African traditional religion, which forms the basis of witchcraft and superstition in Africa. Onen is less critical of the late 19th-century Christian missionaries to Uganda and explained how the protestant preacher Alexander Mackay would throw magic charms into fire to prove they did not work. Onen believes it was the rise of Pentecostalism in the 1950s, however, which boosted Africans' fear of spells and superstition. "Charismatic Christianity is making things worse by over-emphasising it, by advertising it, by lending credence to the validity of claims that witchcraft is efficacious, by fully absorbing that worldview into their worldview," he argued.

When challenged that some Pentecostal churches, such as Watoto Church in Kampala, regularly taught against belief in witchcraft, Onen was dismissive. "I'm not sure how it helps to tell people to not practise witchcraft or to engage in black magic on grounds that it is an evil thing to do while reinforcing the view that it is actually efficacious."

Commenting on the talks, Joanna Sadgrove, a specialist in African Christianity who has researched in Uganda for 15 years, said Onen did not capture the diversity of expression of religion in Africa. "There are religious leaders who capitalise on people who don't have control over their lives. There are also Christians who are doing good works in Ugandan society and being part of a community of faith."

She went on to say: "Witch doctors, child sacrifice and belief in demon possession have been around for years in Uganda, they are just more talked about at the moment because of an increasing western presence in Uganda. Journalists feed a western fascination with these stories and child sacrifice certainly makes the headlines."