I understand the mods' point of view, but I do think that this specific example was a tad unfortunate. I say that because, judging from other reactions, I find it entirely possible that the person who posted the dog story was unaware of it being possibly offensive. Perhaps that person truly thought that the dogs had gotten a happy end in that story (and for all we know, they might have). I'm not trying to argue here, but if I may make a suggestion to the mods: Would it be possible in cases like this (while the thread is still open, of course), that when a mod or admin posts a warning in the thread, that they specify what exactly should be avoided in order for the thread to be left open?
For example, in the Instant Justice thread, the warning would have said "no upsetting content regardless of outcome". Which to some would be obvious, but others might have thought upsetting content with a happy end would be fine. So being more specific could potentially save a couple of threads in the future. (Of course I know that it's impossible to think of everything, but just making the difference between "this was an inappropriate post" and "any post about X is inappropriate", you know?)