It is apparently normal that organisations for social change attract extremists, and many of these organisations fail to guard against the takeover by people who are just more fanatical, and thus dedicated. I've witnessed the same with the german Pirate Party, which used to be about digital rights, and nobody cared. Then it got a few percents at some elections and appeared on the radar. These days, it is about feminism, drug policy, political refugees, city planning and whatever other pet topic some troll pushed through.
Greenpeace always had this activism thing and at the time when the public largely didn't care about the environment, that was probably the right thing to do, to get attention. But as with all things, you have to continuously make it bigger to get headlines again, especially if you have reached your goal and people do pay attention already. And if you go more and more extreme, sooner or later something will break. People die (already happened), or things like this.