It seems to me there are several options which would be more effective, more humane, and more reasonable. They're punishing all dogs and all dog owners to catch a very small few, who are the ones who won't be obeying the new law anyway. In otherwords, this isn't going to solve the problem.
Crucifying the owner of the dog that bit the toddler, fining him, making him pay restitution, and then sticking him in jail would be a better choice. If laws don't exist to let them do that, then those are the laws they should be making.