That's a puppy with "broken legs." My friends and I would never ever break a dog or cat's legs but we joke that if an animal is cute enough it's legs must be broken because we have to pick it up and carry it everywhere.
Reminds me of that test some security guy made. He basically entered people's homes with their consent, acting like a burglar would. In almost all cases the dogs either welcomed him or hide from him. There were very few dogs that approached him in an aggressive way, but even those could be made harmless using a few treats. The truth that many dog owners don't want to hear is that a dog, unless specifically trained for this exact purpose, will very likely not be guarding your home. And if it is trained for that purpose, it will have a level of aggressiveness against pretty much everything and everyone that is not you that it will be both hard to control and completely unsuitable as a pet. Proper watch dogs are more machine than animal.
The primary advantages of having a dog for home defense is detection and deterrence. It will make a lot of noise which will alert you of an intruder and is likely to deter the would-be criminal (not for fear of attack, but simply because criminals don't want attention drawn to their actions).
Yep, that's why a dog alone at home isn't good for anything. It is a tool for a human, who uses its superior nose and ears. If it barks loudly and long enough for a human to hear it (and also not just ignore it. I guess we all know such annoying dogs. ) it can be useful.
An untrained dog will usually let people take their owner's stuff. In a lot of cases, an untrained dog will probably not do anything useful. Now, if an intruder is physically harming the dog's owner, it is much more common for an untrained dog to jump to the owner's defense. Every few months there is a new human interest story about a dog protecting a small child from a snake or some other natural hazard.
Yep, dogs don't really care for property unless it is their favourite toy or food. They do support their pack members though.