"This would likely be seen as an excessive use of the anti-terrorism laws, which were ultimately not designed to interfere with a protest in a democratic society."
LOL Only the brain dead can look on intentional and blatant vandalism as "protest". Green Peace may have good intentions, but as the old saying goes, the road to hell is paved with good intentions. Green Peace is often involved with actions which result in destruction of property. They are NOT a legitimate "protest" organization. Their methods are extremist. While they have not (yet) actively targeted people, many of their methods reveals they do not care if people get hurt as long as their message gets publicity.
Disbanding Green Peace may be going a bit far. After all, we do believe in the right to free assembly. However, the governments of nations world wide need to start prosecuting actions of vandalism and destruction. They need to go after the leadership, since they openly condone illegal activities, as well as any and all active participants in these kinds of actions. Hit them criminally and civilly. Make them pay for damages done - maybe people will get tired of their donations going to pay off fines imposed for vandalism. Maybe if the current leadership and extremist activists gets their useless asses tossed in the pokey where they belong, any remainder who believe in the message of Green Peace, but willing to stay within legal means of expressing their message, can take over.