Don't forget Brent Spar: when they occupied the platform and took some measurements, it turned out Shell was actually right, so they fudged the numbers rather than admit their mistake. Greenpeace is not about the environment any more, even though many of its individual members and employees may still be. This often happens to such organisations: at some point it's no longer about the founders' goals, but about membership, money, and influence. Greenpeace is no exception: today they are a marketing firm with themselves as sole customer.
I am sure they will offer up some excuse about Shell greenwashing its image, or brainwashing our kids about the blessings of fossil fuels, but the stark truth is that this does nothing for the environment. This announcement comes in time for GP to further their real goals: they have been out of the news for a bit and they needed a win and some publicity. Well played.