Discipline isn't about showing a dog who's boss; it's about taking responsibility for a living creature you have brought into your world.
Having pets can teach us a lot of things. For kids, they are often their first lesson in responsibility, and being responsible for the well-being of another living thing is actually great for anyone, kid or adult. It teaches empathy, consistency, and so much more - especially if that pet is a dog.
All dogs can become aggressive, but the difference between an aggressive Chihuahua and an aggressive pit bull is that the pit bull can do more damage. That's why it's important to make sure you are a hundred percent ready for the responsibility if you own a 'power' breed, like a pit bull, German shepherd, or Rottweiler.