I mean...violence is bad.

I don't know why you chose the title you used. I would've upvoted this post but i couldn't because of the title. Violence absolutely is the right course of action in certain circumstances. Violence should never be used first, but once all non-violent means have been tried and failed to correct a grave injustice, then violence becomes the appropriate action for any moral person.

If you do nothing while you watch a murderer kill an innocent person, then part of the guilt falls on your hands. As the saying goes "the only thing necessary for evil to triumph, is for good men to do nothing."