I've never met a rotty yet that wasn't as daft as a brush, but then I don't court the company of people who would have untrained dogs in order to make a statement.
Unfortunately, like mastiffs, staffies, dobies and GSDs, there's a breed of owner that keeps them because it's supposed to show the rest of us how tough the owner is. The owner effectively allows the dog to give in to its wilder instincts, which aren't that far below the surface for any dog. These are the people who fail to understand how much more intimidating the presence of a dog can be when it's lying quietly beside you, waiting for your command.
Whilst walking my own dog (a border collie cross), we regularly meet a large, very boisterous young dobermann out with his 'dad', or sometimes 'grandad'. He's adorable, well-trained and not a danger to anyone, simply because his owner has taken the time and effort to care for his dog properly and understand its needs.