Brutality does not make for an unstable dog... affection does.  Affection will train a dog and when misapplied will make the dog increasingly unstable.  That is why there are so many unstable dogs, affection given at the wrong time.  A dog will deal with brutality, it is an animal and lives in the moment.  Animals react and are trained to react and affection will nurture the reaction.
 
I leave my dog alone until it is calm.  I don't feed it or let it out my front door until it is calm.  So I have a calm dog that listens to me because it is not excited unlike most dogs.  An excited dog will not follow direction and is not in its natural state.  People used to know this but now it's lost and that's why there are so many more problems related to dogs.