Protesters need to find a legal means in order to get what they want. The World War II memorial has nothing to do with the pipeline. It is unfair to the many people who fought and died in World War II that they would have their memorial ruined. People need to be more thoughtful to others.
If a protestor is proven to have done damage to property they should be treated the same as anyone else. In this case, we do not know who did the damage, and it could just as easily be someone trying to pose as a protestor and confuse the situation. Part of peacefully protesting (as it is protected by the first amendment) includes doing no harm to property.
Peaceful protest is a great way to show how you feel about a topic. Peaceful protest is something that is a right in the United States. Many protests start peaceful, but turn to vandalism. During a protest, emotions are involved and when emotions are involved, a protest can get out of hand. Regardless of what a person is protesting, property damage should not happen. If it does happen, an arrest should be made.
Cliven Bundy and his ilk did a crapload of things that could be considered damage or vandalism and they didn't get punished. Yes, protestors shouldn't be able to destroy property without consequences, but everything should be considered in context. In this case, the Vietnam Veterans Memorial is a symbol of so much sacrifice and the pain of so many, so if protestors are deliberately damaging it, there should be consequences.