Clearly D&HM has never had a tiny breed of dog. They bark because they can. They do not need a reason.
My first Yorkie’s name was Berkeley. aka: Barkeley.
The current pair of Yorkies are, collectively, known as: The Yappers.
You cannot compare a toy breed to a larger breed.
Telling a tiny dog to not bark is pretty futile. My dogs will stop barking when I tell them to, but barking at perceived threats? It is in their nature. Or barking because they want attention? Perhaps they think they are too small to be noticed unless they vocalize.
OP, I have found that effusively praising the dog, telling him how good he is, and how glad you are that he has chased off the bad men is a very effective way to handle barking. When you do, they will come running over for a pat, feeling very important and validated. If you talk to the in a harsh voice, then you become part of what scares them.
You can limit barking (see above – it really works), but you cannot stop it, and anyone who thinks that more exercise or training is the answer has not had a toy breed dog. You need to understand their brains and appropriately respond to how they are “wired” I know it sounds counter-intuitive, but praise works. Disapproval? Not so much.
PS: My Yorkies are farm dogs and they get plenty of exercise. When they come in, they are tired. But they will still bark at a sound or ??
PS: A debarked dog (or a de-whinnied horse 
) sounds like a very hoarse person trying to speak. Yes, it is a ‘scratchy’ sound, but it is much easier to deal with than constant loud/high pitched barking is.
