I've always been a supporter of bans on large dog breeds. Being randomly attacked from behind by a German Shepard will do that to you.
Its not that I don't trust large dogs, or think that they are inherently violent (though some breeds are more docile than others). Its the owners I don't trust. I've always believed that generally speaking, humans are too stupid to be properly responsible for another creature.
And now we have proof!
According to Joaquín Pérez-Guisado, the main author of the study and a researcher from the UCO, some of the factors that cause aggressiveness in dogs are: first-time dog ownership; failure to subject the dog to basic obedience training; spoiling or pampering the dog; not using physical punishment when it is required; buying a dog as a present, as a guard dog or on impulse; spaying female dogs; leaving the dog with a constant supply of food, or spending very little time with the dog in general and on its walks.