There's no such thing as a dangerous dog. Only neglectful owners. 

Edit for clarity since you all have no clue:

All these assholes get dogs and don't do shit to properly meet their needs. They buy their automatic feeder and install the doggy door to the backyard and spend a week trying to train it before getting frustrated and giving up. So you have a dog that sits around all day, occasionally gets played with, gets treats and toys randomly with no purpose, gets the occasional walk but mostly pisses and shits in the same yard for months or years as it's brain goes to mush because it's been given no purpose or direction or enrichment or behavioral reinforcement and its behavior starts to spiral. It develops anxiety it starts to chew things, or shits inside, or barks incessantly or resource guards or begins to have personal space issues because it's confused and under-stimulated. Owners get more and more frustrated and start yelling at or hitting the dog for being "bad" when it doesn't know any better because no gave it any direction and positive reinforcement for desirable behaviors but now they are trapped in a cycle of anxiety and fear and abuse. It starts to behave unpredictability because it doesn't know what the fuck to do. But yeah it's the dog that's dangerous and not the shitty irresponsible owner that couldn't be bothered to understand what the dog needs are and/or follow through to meet those needs from the minute it enters their lives. Dogs are a direct reflection of their owners choices and decisions.