One of my best friends was my purebred German Shepherd that weighed about 105+ lbs on any given day. He was adopted from an animal shelter at approximately the age of 6 or 7. They weren't sure of his exact age, as he was found wandering around in a neighboring town by animal control.
He loved to ride in the car and was very easygoing and calm. In fact, he was the only dog NOT barking and going nuts when we walked in the shelter. That's how I knew he was a great dog.
Unfortunately (or fortunately) German Shepherds are a pretty intelligent breed. He watched me operate the fence latch a couple of times and that was all it took. Walked in the door one day, went into the backyard to greet him, and he was gone. He decided he would rather roam the neighborhood in the daytime. <img src="/images/graemlins/grin.gif" alt="" /> A padlock on the latch quickly solved that.
Okay, I am getting long-winded. I've been around plenty of dogs and I'm a dog lover. But I've been hiking before and some moron decides to let their dog run out far ahead of them on the trail. Sometimes it makes for a little "pucker factor" coming around a blind corner. I like when dogs can run free, too, but as others have mentioned, there are only stupid OWNERS.
If someone had shot my dog when he decided to sneak out and roam the neighborhood, I'd be pissed. But his responsibility was still on my shoulders. I just underestimated his IQ (dogs are probably smarter than us anyways).
On the other hand, if I encountered a dog being overly aggressive and wanted to bite, I would defend myself. Whether that's pepper spray, a large stick, a close-by rock, or a .40 S&W round. I'm not going to be crippled or dead because someone decided to let Rover roam free that day. I wouldn't fault anyone else for doing the same thing.
(p.s. - that "Dog Whisperer" show is great if you get a chance to watch it.)