Jupiter: Big brother or big bully?

Some older theories suggest that this biggest gas giant planet in our solar system is our big brother that going to protect our planet, Earth. In 1994 we would wiped out by the Shoemaker-Levy comet but it went into Jupiter instead. However the newer theories said that Jupiter is actually the big bully instead. It also the main reason why Earth was hit by a 10 KM long asteroid or a comet 65 million years ago that killed the dinosaurs. But I agree it may be both.