The dark ones are explained in more detail in the book. And the reason why it's so hard to get a clear picture of things in the game is because it's hard to get a clear picture in the book. Everyone Artyom meets in the book have a different view of what is happening and why.
**** Huuuuge spoiler if you haven't read the book or played through the entire game. Do not read if you want to play the game or read the book****
**** Huuuuge spoiler if you haven't read the book or played through the entire game. Do not read if you want to play the game or read the book****
The Dark ones are never really fully explained in the book (or at least not to my recollection). But they do explain the intentions of the Dark ones. Just before Artyom blows up the dark ones (which is one of two possible endings in the game) in the book he receives a vision from the dark ones where they explain what they've been trying to do. They never wanted to fight the humans, they tried to contact us, but whenever they approached any humans they were gunned down without any questions. After a while the dark ones simply gave up and made the decision that the violent humans had to be putted down. No humans seemed to understand them, until they found Artyom which gave them new hope for peace. But Artyom couldn't get a clear picture of what they were saying until the missiles had been launched and it was already too late. Artyom could only watch as the dark ones blow up moments after he had realized that they could have helped the humans rebuild their civilization.
The second ending in the game let's you "correct" the "mistake" in the book-version and you will be allowed to stop the rangers from killing all dark ones. I'm pretty sure this ending is not available for everyone though. I think it's only available for players who has tried to approach the dark ones in the visions and has done good deeds (like giving ammo to the poor, refusing rewards, saving people etc).
The second ending in the game let's you "correct" the "mistake" in the book-version and you will be allowed to stop the rangers from killing all dark ones. I'm pretty sure this ending is not available for everyone though. I think it's only available for players who has tried to approach the dark ones in the visions and has done good deeds (like giving ammo to the poor, refusing rewards, saving people etc).