One of the dogs I have killed was trained. Still stupid dog. The owner was pretty upset that it was so easy to kill his "killer" dog. Trained dogs are over rated normally - makes for good TV though. Usually criminals just feed them poison, or use a club. About the only thing a guard dog does worth anything is bark. They are really good at getting you sued too if someone ends up on your property trying to retrieve a ball or something.
They may be fearless - but so what? It is much easier to deal with a dog straight at you than one that will sneak up behind you and nail you without warning because it is a coward. By the way - they are not fearless - they just act like it. Fearless when facing the dominate predator of the world that outweighs you two to one would be insane. Unless that predator starts to run.
One thing that concerns me when people talk about dogs is that think "pet" not "predator". If a dog is being aggressive, you had better know when it is being a predator - and you don't want to act like a prey. You also don't want to act like you are a beta male - good way to get bitten.
If someone has a trained dog out loose - the cops need to be called.
Most dogs are fine and friendly - but I really watch out for the purebreds. Many of them are inbred and have genetic problems, especially in the hips. Makes them very bad tempered - and scared. Germain Shepherds are in this category. I prefer mutts for dogs - good natured and healthy.
Had a dog bark and snarl at me today but it was my fault. He was sleeping in the road (bad idea) and I thought he saw me - nope, not until I was nearly on him. I scared him pretty good I am afraid. It was my fault. I say this to point out that many dogs are not an issue - most of them are not, and I really am a sucker for dogs. I really like them. However, not enough to let one bite me.