I did read the book Timber, just a few months ago in fact , and Orson did not just attack one person. He attacked several people, his behavior had become more and more unpredictable, with an escalation of aggression, and Katz had tried everything, including trainers, traditional and non-traditional veterinary care, as well as some pretty far out stuff, to try and figure out what was wrong in his dog's head and what to do about it. He didn't just give up and toss him aside at the first hint of a problem.
I don't know if I'd have had the courage to do what he did, but he didn't feel like he had a choice, and under the circumstances, I can't fault him. If it had been my dog I would have been very afraid that he might seriously hurt someone someday.