Yeah, no kidding. Of course, everyone is going to blame the owner. No, people - sometimes animals (and people!) just end up bat-shit. While I don't agree with everything my wife does with regards to raising animals, she's pretty good at stomping out aggressive behavior. That cat was just in-fucking-sane. No doubt about it. The cat in the ad - same thing. And yeah, per the last paragraph in the ad, they've obviously been getting a little hate mail.
I feel for the owner - you feel trapped. Though you may have had homicidal thoughts at times, actually having the cat put down is the last thing you want to do (or, rather, the last thing you want to make the call on). Shelters and rescue centers won't take them. We found a vet that, similar to the one in the ad, never saw the bad in him. They offered to take him for a fee. I doubt he made it more than a couple of days. I had NO love for that animal, but my wife did. I felt bad for her, though after several years of dealing with that thing, she realized it was a lost cause.