Animal abusers are more likely to commit violent crimes against people

Animal abusers are five times more likely to commit violent crimes against people and four times more likely to commit property crimes than are individuals without a history of animal abuse.Many studies in psychology, sociology, and criminology have demonstrated that violent offenders frequently have childhood and adolescent histories of serious and repeated animal cruelty. Research has shown consistent patterns of animal cruelty among perpetrators of more common forms of violence, including child abuse, spouse abuse, and elder abuse. In fact, animal cruelty is considered one of the diagnostic criteria of conduct disorder.
If you break it down to its bare essentials:
"Abusing an animal is a way for a human to find power/joy/fulfillment through the torture of a victim they know cannot defend itself."
Now break down a human crime, say rape. If we substitute a few pronouns, it's the SAME THING.
"Rape is a way for a human to find power/joy/fulfillment through the torture of a victim they know cannot defend themselves."
Now try it with, say, domestic abuse such as child abuse or spousal abuse:
"Child abuse is a way for a human to find power/joy/fulfillment through the torture of a victim they know cannot defend themselves."

The line separating an animal abuser from someone capable of committing human abuse is much finer than most people care to consider. People abuse animals for the same reasons they abuse people. Some of them will stop with animals, but enough have been proven to continue on to commit violent crimes to people that it's worth paying attention to.
Virtually every serious violent offender has a history of animal abuse in their past, and since there's no way to know which animal abuser is going to continue on to commit violent human crimes, they should ALL be taken that seriously. Animal cruelty is not a harmless venting of emotion in a healthy individual; this is a warning sign... It should be looked at as exactly that. Its a clear indicator of psychological issues that can and often DO lead to more violent human crimes.
A person feels powerless and develops a warped sense of self-respect. Eventually he/she  feel strong only by being able to dominate a person or animal.