Keeping those Commie Comets at Bay!
I don't want either war or weapons on Earth or in space, but until the day comes that we all live in peace and brotherhood (any time now...), I see no reason why we shouldn't remain prepared for any problems.
All one needs to do (I know, I'm making this sound easier than it is, but hang on) is attach a rocket motor to a small planetoid and aim it at Earth. Even one 0.5 mile across could be devastating. I know I certainly would like us to have the technology to destroy or deflect such a threat, natural or otherwise.
I say Yah Deep Impact!