There is a woman in my town that has one. And when they were banned the news interviewed her, and she said it's because the dog makes her feel safe when she walks the streets at night.
People buy them to be aggressive, it's ridiculous. If it's a choice between a dangerous dog and allowing people to have guns I honestly would rather that they had guns. At least the gun is controlled by a somewhat competent human, the dog is unpredictable.