While I will not go so far as to say that violence can be a good thing, it is sometimes a necessary thing. Unfortunately the fight for freedom has often erupted into violence, and without the violence freedom and fair treatment would never have been won. Communication should always be the first attempt, but some things are important enough to fight or die for.
Most situations in life do not really require violence. A verbal dispute does not need to end in violence and can be often resolved through words or patience. Teaching that violence is a solution just causes more violence. The only time violence is acceptable is in direct self defense, especially if the target cannot be reasoned with.