It's a terrible thing when someone is hurt or even killed by a dog. I can understand that persons loved ones wanting the dog put down and I can see the need for having that particular dog put down, but these are only reactionary measures as are blanket bans on certain breeds and encouraging people to dob in others that may have a violent dog.
What we need to do is limit the cases of dog attacks, and this, as in anything, can be done with education. Information sheets given to any knew dog buyer on the nature and care instructions for their breed as well as their responsibilities as pet owners, and the laws and regulations that go along with owning a dog, with links to government (or other related) websites, could contribute to change. The problem is, not everyone will bother to read the information sheets or take the information on board. Therefore other, more prescriptive measures, could be implemented to prevent dogs from becoming violent, restrictions on breeding and selling, a requirement for potential dog owners to be licenced (similarly to reptile owners), or even a requirement to file proof of attending at least one dog training session after purchase. All or any of these things can reduce the number of neglectful, irresponsible or simply unknowledgable dog owners creating violent dogs, and by extension prevent deaths both human and canine. Responsible dog ownership should be the goal and knee jerk reactions will not contribute to it.
P.S. Sometime earlier this year I did a post in Dogs in Myth if you want to check it out.