2. The McFly's Would Have Stayed Complete Losers
The Movie: Back To The Future Trilogy Forget the DeLorean repeatedly breaking down. Not only would Marty have not been able to get away from the hyperbolic terrorists alive, thus destroying the story for the entire trilogy, but it's a good thing time travel in the Back to the Future movies doesn't Swiss-cheese anybody's memories (hey, that's applicable, right?), because the characters would have had a heck of a time getting anywhere after each trip, even when pushed by a train. It seemed deeply serendipitous that Marty was able to escape into the past in the first movie, showing that even in a story focused on the nature of cause and effect, anything can happen nevertheless, over and over and over again.