why massive asteroids are bad

 A massive astroid wiped out the dinosaurs. That drastically changed the habitat of earth too quickly. Generally fast change to the earth is destructive and kills lots of life here.

There could be other "end of the world" events, but the Bible indicates that a flaming mountain will hit the ocean. Then there are a series of devestating events that kill large numbers of humanity. This is from the book of Revelation.