Think about these scenarios: You are walking home at night. You notice a figure following you. She appears to be stronger than you, and is very large in terms of muscle. As you turn a corner, she grabs your arms and pulls out a gun. She is too strong to be disarmed, but you do keep a gun in your holster and she hasn't noticed it yet. Do you defend yourself? And now this. You are in Germany during World War II. You are in the Fuhrur's office. Hitler is at his desk, too busy with paperwork to notice you. You have a pistol in your hand. Do you use it and end the war? This doesn't mean all violence is acceptable. Just context.
Imagine this. A radical actor who strongly opposes the president of the United States is in the crows with a gun pointed at the president of the United States. Their figure is in the trigger guard poised to shoot. The crowd is very loud so the president cannot hear you. Do you shoot the actor or let the president be shot at?
I bet the if it was so great a cause you could find a better way to solve it. People dont need to be mean to get what they want. You should never hurt someone for a greater cause. If you want that greater cause so much why not find a better way to do it. If someone found out that you had hurt someone for the cause that would mean you were in big trouble.