Watch the video again please. Better yet, google for the longer version that shows up close the deep bite marks in the childs flesh, with visible muscle tissue. This was not a quick bite or nip. Similarly, even in this shortened clip you can see the dog "stalk", approach, bite, and drag the child across the lawn. A child that was on the opposite side of the car from the dog and was approaching his own home.
It's precisely because the dog "has no idea what he/she did wrong" that it sadly needs to be put down. If this level of aggressive is "second nature" to this particular animal, it really has no place in a suburban community.
Not all things deserve to be in all places at all times. Even in good ol America. A dog with proven history of a vicious unprovoked attack on a child is, in my mind, one of those entities. And I'm a dog lover.
Yes, the owners failed the dog. But the owners did not attack the boy. The dog did. And likely will again if given the chance, this kid or some other.