Pit bulls are a risk that society no longer wants to take

The Globe and Mail: Ontario bans pit bulls
My sister and I have had lots of arguments about this kind of legislation. She is a dog trainer who has an almost magical ability to work with dogs, and with their owners -- she know a lot about how dogs think, so she can often figure out some way that an owner can deal with dog misbehaviour, or just dog annoying behaviour, and she does a number of individual consultations with owners who are at their wits end in dealing with a doggy problem. Anyway, she disagrees with anti-breed legislation, saying it is the owners that are the problem not the dogs.
Pitbulls are not the only dangerous breed around -- shepards, spaniels, labs, dobermanns, rotweilers, can be abused and can become untrustworthy. We own two yellow labs, and I know how strong these dogs are -- if they wanted to take off, I would not be capable of holding them back physically. But they are good dogs to work with, and they listen to us -- and we have trained them for bite inhibition, which all owners of dogs in a city should do.
And we have also gone through the agony, a few years ago, of putting a dog to sleep which we had got from the SPCA, which turned out to be so emotionally damaged by his previous life as to be untrustworthy around children.
But pitbulls have a tenacity in fighting that most other breeds do not have, and also seem to be the dog of choice for the worst owners. While I agree it is the owners that are the problem, I feel that society can no longer take the risk with strong, potentially violent breeds like pitbulls -- the consequences of bad ownership are too horrific.
If a bad owner owns a dashund or a toy poodle, well, so what if they jump up and bite you on the kneecap?
But if a bad owner owns a pitbull, that dog can kill a child. The other benefit of this legislation is that it will stop the unprincipled breeders who are breeding and selling these dogs.
Anyway, that's what I believe. But my sister also sees the tragedy of the dogs who could be saved if they only had owners who cared.