It is much harder to make something hit something in the vastness of space than to make it miss. Only a very small portion of the orbit changes that could occur from an experimental impact would move an object towards Earth. The chance of doing it by accident are extremely small. Of course any planning should make sure that is not a possibility, but this is an argument that should be squished flat before hysteria mongers like BD or the Cassini Cooks get traction on it. Sagan opposed an asteroid defense system for similar reasons, but asteroid experts laugh at that stance.

Regards,
Mark