If you build a system that has a high likelihood of breaking the law in normal expected use, and then it's found to break the law, shouldn't we disincentivize that in some way? Is that just blaming the researchers/developers, or is that just making people respect the law?

I think the important thing to note in both dog attack scenarios presented is that the owner is responsible in both cases. Either they purposefully created an unsafe situation or they were negligent in protecting the public from their property. Whether the dog is euthanized is about preventing it from happening again. Preventing it from happening in the first place is done by making the owner liable to disincentivize it.