I think that people must not take fighting dogs as pets. Or these owners must be very responsible for special training of their dogs and watch them very carefully. Owners who don't look after their dangerous dogs good enough must be punished (a jail is crying about them...).
I have a 8-years-old dog. Great Dane. This is a very friendly, very calm dog, good trained in a dog school, and I trust her very much. But I never allow her to run without lead if anybody is around me. People can be just scaried.
I do not understand why some people give a lot of freedom to Bullterrier, Bullmustiff, Staffordshire Bull Terrier or Akita dog only because they (owners) think that their dogs are kind and friendly (They say:"He is 5 years old, and we never had any accident with him"). Stupid people! Don't they know that they shouldn't trust these dogs? Nobody knows what they will decide next minute! Before buying a dog, everybody should ask, "Am I the person for this dog?"
Every dog can become dangerous in bad hands. Owners of big dogs should give particular attention to their pets.
I am against killing of old dogs. May be only if they(dogs) are paralized, I can understand the owners.