You certainly have a good understanding of how people behave, Tom. You are right—there is a strong connection between a person's tendency toward violence and the way they treat animals. Parents, teachers, and friends can all help a person to change. Sometimes negative consequences, like getting punished for hurting an animal, persuade people to control themselves better.
It also helps to educate people about how animals feel fear and pain just the way humans do. If you are worried about some one's violent temper, I suggest you find someone to tell who you trust, and who would understand your concern. It is very hard to deal with a violent person all by yourself.