I dont know what the feelings are out here is on heavy metal, but I thought Black Sabbath's "Children of the Grave" is a great song and is what we are looking for. It's primary message is clearly the fight against existential risk. It also portrays the nature of the situation very well, sending across a very clear message. It certainly lacks any technical sounding language, which may be what is needed if something were to be adopted as an anthem, especially for this kind of movement (that is already viewed as being way too technical).

You can check it out here.