It's not about the environment and has not been for years. They are called "Watermellons" for a reason. Green on the outside, red on the inside.
Patrick Moore, one of Greenpeace's founders, left the organization after it became clear to him that the organization was no longer an environmental organization, but a political organization cloaked in environmentalism.
Why I Left Greenpeace
It becomes easy to understand these organizations once you realize that they don't actually care about the environment. They simply use green language to achieve non-environmental political goals. Their actions then make a lot more sense. Once you understand their motivations and methods, then it becomes that much easier to thwart and oppose them. Once you know their position is the unscientific and illogical one it them becomes trivial to shoot down their arguments.
Much like how MADD morphed from a drunk driving awareness organization to a neo-prohibitionist organization. (Whose founder also left the organization is disgust.)