Thanks! I was beginning to think I was the only person that could see that a thermonclear explosion in a vacuum isn't going to do much. On the other hand, they could go out to an incoming rock with some of the solid-fuel boosters from the Shuttle and deflect it.
Weeell, it's not quite that simple. A well placed (at the proper distance from the surface) 'explosion' will deflect a mass. That is hard to do.
The burst must be in the right direction on a body that will be rotating about all three axes. That is hard to do.
The machinery has to reach the body in a timely manner. That is hard to do.
We aren't even sure of our ability to reliably detect Earth crossers.
The product of all of these uncertainties is HUGE.
The conspiracy of ignorance masquerades as common sense.