We're Doomed... Maybe

I like the idea of having a missle defense system in space. It seemed to have scared the Soviets badly. But, can we make sure that it points towards space as well? Because we really should be trying to prevent this sort of thing.

UPDATE: In another report, the chances are 1 in 42. But it won't end civilization, just cause the havok of a typical nuclear blast.

UPDATE AGAIN: At one point this thing was at 1 in 37, but now it's considered a negligible possibility. This does not comfort me. If we have so little ability to predict asteroid strikes, how can we know which ones need to be stopped?