In a human domestic environment, we would like as little aggression as possible, even of the most ritualized sort, directed at us. To achieve this standard, it is important to both understand the roots of aggression and to intervene with pro-active prevention programs for all dogs. When a dog is uncomfortable around strangers, or dislikes certain strangers, such as men, kids or uniformed people, it is usually because she has not been fully socialized. A socialized dog is relaxed about the elements in her environment. To become socialized, a dog must have sufficient exposure and positive experiences, especially when young.
Socialization can be specific, too.
A dog may be socialized to toddlers, because she grew up with toddlers at home, but not be used to teenagers, or to babies. Aggression comes into the picture when the dog encounters something she is not socialized to. She will be highly motivated to increase the distance between herself and who or whatever is making her uneasy. The underlying motivation is anxiety. When you think about it, almost all untamed, unsocialized animals are neophobic.