I'm all for peaceful environmental protesting, but destruction of property and historic monuments/items only makes your movement look worse. News will spin it as the protesters being vandals and go about their day. Most people won't think beyond that and will probably associate environmental activism with negative things such as vandalism or whatever else their favorite news calls what they're doing.
There's no need for the media to spin anything, the protestors committed vandalism and, unless they are protesting the existence of prehistoric monuments, they did a really shitty job of even calling attention to their cause.