I think this returns to the human idea related to this - are we all born with the same potential and it's simply a matter of upbringing?
I personally would say no, there are things inherent in ourselves that set us apart from others, attractions, aptitude for learning, physical strength, height, weight, temper. Sure, these can all be affect, shaped and changed by upbringing and training - but those that are fundamentally 'stronger' in one area are always going to be stronger if they train it, no matter how hard the 'weaker' trains.
But to make my point clear: Dogs, just like humans, are born with variations, some stronger, some smaller, some weaker, some bigger, some more temperamental, some more docile - it does no one harm to ban the ones that are overtly strong and violent. That's not to say..wipe them out, 'cause that's like wiping out an entire species. But make them illegal for personal ownership - especially if they're going to be trained to use that strength against intruders and babies.