I should clarify my last post.
Agression is more common in some breeds, like maltese for example. (not so much a case of past breeding for agression, but dogs with certain tendencies and instincts, which are compounded by owners who dont train or react properly to bites, as they dont believe they are dangerous.
But some breeds have been bred in the past, with agression as a trait.
This is no longer the case, but these breeds, when not trained or cared for properly, can show these traits.
It is up to owners of these breeds to provide basic training, and proper care, which most do.
Unfortunatly these breed attract morons who only want them because of their 'tuff' image, and fail to provide proper care. This, in alot of cases, is what can cause an insecure, and stereotypically agresive dog.
Of course, any moron can make ANY breed of dog agessive with the wrong treatment..
I was just sharing my exp with sheps, which although I have known very nice ones, I have been attacked by a few in the past, and it has tainted my view of them, not to say that they are bad dogs, just they are no longer attractive to me.