I've heard that "blowing up" asteroids as seen in films would be ineffective, as it would turn the individual object into a shotgun spray of smaller asteroids with a larger perimeter. Which would be more likely to damage our planet. But what about firing rubber bullets (or objects with little destructive power, but decent kinetic "knockback") to slow down the asteroid or knock it off trajectory? I've never heard of this idea so I assume it has obvious flaws. What are they?