It could be dangerous because it could inflict more damage than say, a chihuahua. But size has nothing to do with how aggressive a dog is.

Actually, most small dogs are more aggressive than large dogs because of "small dog syndrome" Basically the small dogs have giant egos and think they are huge. But they would do way less damage than a very large breed dog.

My dog is mastiff and huge, and the sweetest thing, even though she is large and powerful.