I think it really boils down to an essentially species-wide psychosis, paranoia, and overall misconception of our own worth to the planet, or even the universe. This planet has so many fascinating lifeforms on it. Even if humans were to die out, even if the whole planet were to be annihilated, it is naught but the tiniest of specks to this solar system. Likewise, were the solar system to end, it is a mere particle to the galaxy, which is absolutely nothing to the universe. The universe would continue and not even notice something which has happened infinite times before. That all being said, it is inevitable that the world end, but not necessarily inevitable that the human species end with it. Scientists are making a sort of high tech Noah's Ark by freezing DNA from all manner of creatures and plants. It is possible that we will take that information and colonize other moons, planets, or artificial space stations. Even so, eventually an end will come for humans. Every time a religion predicts an end date, that day goes by with nothing. This has happened for thousands of years. At some point, if they say tomorrow will be the end enough times, they will be right.