Well, I don't know about other countries, but in Nigeria, Islam has hardly seemed to be a blessing. First of all, someone said Islam led to a golden age in West Africa, maybe so but the great Kingdoms in Southern Nigeria were founded on African religions and not Islam.
There was also a Jihad led by the Islamic scholar Uthman San Fodio that forced most of Nothern Nigeria to "reform" and was only stopped in the Southern city of Ibadan. It's also been one mess after the other since independence, the worst atrocities now being committed by Boko Haram.
So yes, I agree with op when he says that Africans need to start questioning whether these foreign religions do more evil than good.