It is believable that they're trying to delete us in order to save the planet. But killing is never the answer.
It all comes down to the question: is the human race more important than this beautiful planet? Would you wipe out our entire race, so that Earth can finally breathe and exist in peace (ignoring the possibility of another race occupying Earth)? Keep in mind that without Earth, there's no humans. But there can be an Earth without humans.
By the way this perfectly matches the Walt files.