Tamborine you talk a load of unadulterated cr*p. For a start the pictures you gave are of Bullmastiffs, which are neither Mastiffs or Dogue de Bordeaux, and the Mastiffs are one of the most gentle of all large breeds. They are not as a breed cowardly, neither are Bullmastiffs or Dogues.
There can be rogue dogs in any breed, and unfortunately due to their size if you get one that is not socialised or trained by a responsible owner it can be a menace. This does not mean you should condemn the whole breed.