Violence exists in our Universe, and is inherently random. If we want to protect ourselves from it, we must understand it. If we want to understand it, we must study it. If we want to study it, we must look at it, take it in our hands, pick it up, and examine it in minute detail from every angle. Rather than examining it physically, we examine it mentally, by visualizing it and safely modeling the results.
Along with understanding, we must have proficiency, not in "defending" against violence, but in using violence. Violence backed by extreme intent cannot be "defended" against, it must be stopped. It is for the times when it can only be stopped by superior violence that our training is intended to prepare for.
In other words, we are training to prepare for our own hypothetical attempted murder.
If we take "violence" to mean not just intentionally "hurting" but intentionally causing injury, then injury is the ipso facto fruit of violence, serial injury is the result of sustained violence, and death is the inevitable endpoint of serial injury. In other words, the line between injury and death is imaginary; it is simply a slippery downward slope from one to the other.
Therefore, there is no difference between training to injure and training to kill; they are functionally the same. This applies whatever the particular tools or methodology applied to the task happen to be.
If you chose to carry a firearm for personal protection, it would behoove you to take a firearms safety and training course. You would learn not just how to keep yourself and others safe, you would learn how to use it as a tool for applying violence, i.e. you would learn how to use it to intentionally injure (read: kill) people. You would train by placing a representation of a human silhouette on a target and then repeatedly using the tool in the way it is designed to be used: draw, aim at center mass, and fire, over and over again, until there is no mystery or apprehension remaining about the process, until you can do it as comfortably and easily as tying your shoe.
We train to use our bodies in the same way and for the same reason. All of us are walking around armed with the deadliest weapon in existence, the human brain, and a supremely effective tool for effecting its will, the human body. We train to learn the capabilities and vulnerabilities of our tool, so that we can protect ourselves and others from injury, whether intentionally or unintentionally applied, including being able to apply it effectively ourselves when that is the only way to effect the former outcome.