Very agressive dog breeds.?

Why is the desire to own such animals so prevalent at the bottom end of society. Is it lack of even common sense or an interest in dog fighting or what? And why oh why are all such animals not banned completely?
Update: Many bad if not fatal attacks are unexpected often by well loved pets and experts have concluded that breed nature can be a factor. I have not pinpointed breeds because a) I am not an expert and b) It is not needed to gain the information requested.
Update 2: Some answers are emotional and attribute things to my question which are not present. You may love dogs as I do being from a farming family and a 'I love all dogs so you have no right to ask this' attitude merely neutralises your opinion. Personally I have more regard for the children killed and am only... show more Some answers are emotional and attribute things to my question which are not present. You may love dogs as I do being from a farming family and a 'I love all dogs so you have no right to ask this' attitude merely neutralises your opinion. Personally I have more regard for the children killed and am only too willing to agree that 9 out of 10 owners do not train their dogs properly to stay in all circumstances without a lead as our working animals were.
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