Good video. Old, but good.
Corgi - Dogs aren't trained to fight. Its either in them, or it isn't. You can't take a dog with no desire to scrap and turn it into a champion pit dog, no matter how much training you give it. Nor are they bred to show the maximum aggression towards the other dog. Simply put, some dogs will puff up and make a great show when another dog comes on the scene, and they end up being worthless as a match dog. And others will remain laid back until put in a pit situation and faced off with their opponent. I think a lot of the old-time dogmen preferred a mellow dog that wouldn't waste a lot of energy trying to find its opponent until you actually put them in the pit. If you listen to some of them talk, they have no use for dogs who will kill puppies and such, because they feel its a sign of cowardice rather than bravado.
Ugh. Gruesome stuff aside... I think the reason folks are more likely to dump Pit Bulls is because of the very high availability. They can get a pup as an impulse buy for $50, dump it, get another, dump it. And like it or not, the situations you described where people can't board their dogs, can't get insurance, are alienated by family for owning the breed; those things contribute to the dump rate, IMO. Its easy enough for someone to get a Pit Bull puppy, say they're going to raise it up right, until they realize that they're getting the police called on them for having a "vicious" dog, or that their kids' friends aren't allowed to come over and play because of the dog. That kind of pressure can sour people very quickly. I had to make sure my entire family was cool with the idea of me getting a puppy, because I knew the kind of strain it would cause if they weren't.
And in all fairness, the breed has a history of dogfighting. Its not just a few dogs. And IMO, its not a bar to owning the breed. You just have to be more attentive. If you don't want a dog that's going to challenge you, this is not the breed to pick. If you want a dog that's going to play nice with other dogs at the dog park, again, not the breed. I agree that you can train appropriate behavior into these dogs, but you can't expect them to act like dogs whose pack behavior has been encouraged through the generations. Its not fair to the dog, or to other dogs around him. When I encounter new people looking into the breed, I always prefer that they acknowledge the potential for dog aggression, rather than feel they can train it out. There are just too many people who get these dogs, raise them together, then are stunned when one day the dogs bloody each other over some unseen stimulus. There is no shame in being prepared, only in avoiding the truth.