Wish Rachel would have answered this, she has wonderful insight on Pitties and rersponsible ownership.
1. Pit Bull type breeds (APBT, AmStaff, Staffie) that have severe aggression are not bred by responsible breeders, and the breeding of such dogs is not condoned by responsible breeders, responsible owners, and the educated public. Yes, pit bull type breeds that have severe aggression should NEVER be bred, should be spayed/neutered, and be placed within a pit bull savvy home with no other dogs. That is, if the severe aggression is dog aggression. If the severe aggression in question is human aggression, the Pit Bull type dog should be put down, or placed with a group (such as Best Friends) that have the time, money, and energy to invest into such a dog to rehabilitate it. Even then, the dog should be court-ordered to never leave that site. That is, if the severe aggression in question is, like I said, HUMAN aggression.
2.No, Pit Bull type dogs are not "supposed" to show any kind of severe agression. Aggression towards humans is against breed standards and is usually due to bad breeding, overbreeding, irresponsible ownership, no training, etc. etc. Severe dog aggression is not condoned either. SOME level of dog aggression is expected, but is not a breed standard, which is why pit bull savvy owners put so much time into training and socialization. Dog aggression was bred into these dogs for generations and generations, as well as a high prey drive (as with most any terrier). The breed standard which calls for dog aggression was for people way back when, when dog fighting was legal, and that's all these dogs were used for. Nowadays, they are family pets, or working dogs, so little to NO aggression should ever present itself with good breeding, strict continuous training, and a responsible owner. So no, the docile ones should NOT be removed from the gene pool, as they are the ones that are needed in the world today.
3. Again, they are not supposed to show severe aggression. With the right training and the right ownership, Pit Bull type breeds should never show any kind of aggression towards dogs or humans. However, Pitties that are chained up outside, with no human contact, no training, and just fed and used as lawn ornaments, those are the dangerous ones. But then again, you could say that about any breed. Take a chihuahua, chain him/her outside, fed it, but never train, talk to it, or socialize it, and see what kind of monster you end up with.
4. Again, severe aggression is not supposed to be present. There should be legislation regaurding pit bull type breeds, but not the kind you are talking about. There should NEVER be a ban on an entire breed in any or all parts of the country/world. There should however be a breeding restiction. Such as only responsible breeders should be allowed to breed, and only so many litters per dog, per every so many years, etc etc. There should also be a competency test and special registration process for Pittie owners, but I think this should go towards all breeds.
5. Ok, responsible owners don't take their dogs out without a leash, into a dog park, etc. if the dog is aggressive. The people who you are asking these questions, who actually have intelligent answers, probably don't own aggressive Pitties, because they are responsible. For example, I own three Pitties. One is around 5-8, one is about 2 and my youngest is 10 months. All are spayed/neutered, and all have been through several different training classes. My youngest is working towards his CGC, which will be taken sometime next Feb.-March. They all go out in public on leashes, but I do not muzzle my dogs. Why should my dogs have to suffer because of the acts of careless people? I feel safer with a Rottie walking towards me on the street, than I do when a Chi or Pom or Poodle is. I have had bad experiences with those breeds, but I do not take that out on ALL dogs of those certain breeds. I don't take my dogs to dog parks. Not that I don't trust my dogs, I don't trust OTHER people's dogs. I know that my dogs would not start a fight, but I do know that they would finish it. I also NEVER leave more that one out of their crates when we are not at home. It's not that I don't trust them, it's that if playing gets out of hand, and I'm not there to stop it I know what COULD happen, and I would rather not come home to a blood bath.
I don't know who it was that said aggression is not only normal but accepted, but they are an idiot. Yes, some tiny degree of aggression should be expected, but that's what they make training for. The right dog in the hands of the wrong owner, can make a very ugly front page news story. I think the answer is education, all around. Get rid of BSL, get more legislation that works, such as breeding restrictions, licensing rules, training criteria etc. etc. and the number of "blood thirsty" pit bulls on the 6 o'clock news, will disappear.