Whatever people think about Greenpeace I think it's a stretch to say they are a plant. They just lost a lawsuit recently and have to pay $660 mil for defamation against an oil company. It was a pretty ugly case.
For a well-established organization like Greenpeace, it becomes increasingly difficult to believe it's a matter of them collectively having an emotional reaction. They have the resources to look at the evidence, and have indeed almost surely done so; when it comes to explaining their refusal to accept that evidence, ”their jobs depend on rejecting it” is a much simpler explanation IMO than “they are experiencing a collectively-identical ideological quirk that their organizational bureaucracy somehow has yet to iron out”.