Violence can be justified, especially to prevent or answer violence.
But the target of the violence matters a lot. Violence against people who have nothing to do with the problem is never justified.
Rebelling against violent police is perfectly justified. Rebelling against a terrorist state that commit atrocities is perfectly justified. All out war against a invader is perfectly justified.
Killing civilians, murdering civilians and taking them postage is not ever justified. This is either war crime or terrorism.