I've come to the point that when people say, "I'm against violence." I think, "That's cute."
"Violence" is a fairly broad term. It's violent to murder somebody. It's also violent to shoot a would-be murder or rapist.
Violence on violence happens all the time. The ethics of the violent acts depend on several factors.
The baseline libertarian position of being against "aggression" makes more sense.
You can use violence against an aggressor. You just aren't allowed to be the aggressor.
It would be a wonderful world if rapists and murderers didn't exist. We don't live in that world.
If you're in a situation wherein you can stop a heinous crime from happening by using violence, and you choose non-violence, your inaction is a moral issue in and of itself.
Is your aversion to violence so great that you would let an act of violence happen in front of you while doing nothing about it? Would you just plead for mercy?
Most of us aren't against violence. Most of the people who claim that they're against violence are lying or stupid. Those few of us who are truly against violence were useless against the Nazis. Those few of us who are truly against violence are useless to call for if you're being murdered, robbed, or raped.